<PAGE>   1
                                                                    Exhibit 10.1


                        THIRD AMENDMENT TO LOAN AGREEMENT

         THE KROLL-O'GARA COMPANY, O'GARA - HESS & EISENHARDT ARMORING COMPANY,
KROLL HOLDINGS, INC., and KROLL ASSOCIATES, INC. (individually and collectively
the "Borrower"), and KEYBANK NATIONAL ASSOCIATION ("Lender"), hereby agree as
follows:

1.       RECITALS.

         1.1      On October 30, 1998, Borrower and Lender entered into an
                  Amended and Restated Loan Agreement (the "Loan Agreement"),
                  which Loan Agreement was amended by an Amendment to Loan
                  Agreement dated as of June 25, 1999, and by a Second Amendment
                  to Loan Agreement dated as of October __, 1999 [sic].
                  Capitalized terms used herein and not otherwise defined will
                  have the meanings given such terms in the Loan Agreement.

         1.2      Borrower and Lender desire to further amend the Loan Agreement
                  pursuant to this Third Amendment to Loan Agreement (the
                  "Amendment").

 2.      AMENDMENT.

         2.1      Section 3.1.1 of the Loan Agreement is amended to provide as
                  follows:

         2.2      TOTAL FACILITY. Lender will make available to Borrower a
                  revolving credit facility of up to $25,000,000 ("Total
                  Facility"), subject to the terms and conditions and made upon
                  the representations and warranties of Borrower set forth in
                  this Agreement. Amounts outstanding under the revolving credit
                  facility from time to time will be referred to as the
                  "Revolving Credit Loan". The Revolving Credit Loan will be
                  represented by the promissory note of Borrower of even date
                  with the Amendment to Loan Agreement and all amendments,
                  extensions and renewals thereto and restatements and
                  replacements thereof ("Revolving Credit Note"). The Revolving
                  Credit Loan will bear interest and will be payable in the
                  manner set forth in the Revolving Credit Note, the terms of
                  which are incorporated herein by reference. Notwithstanding
                  any of the foregoing to the contrary, the Total Facility will
                  be increased from $25,000,000 to $40,000,000 until September
                  30, 2000 (the "Reduction Date"), at which time it will reduce
                  from $40,000,000 to $25,000,000, and Borrower will pay to
                  Lender on the Reduction Date the principal balance outstanding
                  hereunder that is in excess of $25,000,000.

         2.3      Section 3.2.3 of the Loan Agreement is amended to change "May
                  31, 2000" to "May 31, 2001."

         2.4      Section of 5.3 of the Loan Agreement is amended to provide as
                  follows:

                  5.3 RECENT ADVERSE CHANGES. Except as specifically disclosed
                  in the Disclosure Schedule and/or the Proxy
                  Statement/Prospectus, since the dates of the most recent of
                  its Current Financial Statements, it has not suffered any
                  damage,

<PAGE>   2

                  destruction or loss which has materially and adversely
                  affected its business or assets and no event or condition of
                  any character has occurred which has materially and adversely
                  affected TKOGC and its Subsidiaries' assets, liabilities,
                  business or financial condition taken as a whole, and it has
                  no knowledge of any event or condition currently existing or
                  threatened which may materially and adversely affect TKOGC and
                  its Subsidiaries' assets, liabilities, business or financial
                  condition taken as a whole.

         2.5      Sections 7.1, 7.3, 8.12, 8.13, and 14.40 of the Loan Agreement
                  are amended to change all references from "Indebtedness" to
                  "Debt".

         2.6      Section 7.4 of the Loan Agreement is amended to provide as
                  follows:

                  7.4 GUARANTEES. Other than with respect to the Senior Notes
                  and guarantees by one or more of the Persons constituting
                  Borrower of the obligations of one or more other Persons
                  constituting Borrower or of the obligations of any Guarantor
                  or real estate rental obligations of any Subsidiary,
                  guarantee, endorse or become contingently liable for the
                  obligations of any person, firm or corporation, except in
                  connection with the endorsement and deposit of checks in the
                  ordinary course of business for collection or accounts payable
                  incurred by Subsidiaries in the ordinary course of business.

         2.7      Section 7.5 of the Loan Agreement is amended to provide as
                  follows:

                  7.5 INTEREST COVERAGE RATIO. Permit the ratio of Borrower's
                  consolidated earnings before interest and taxes divided by the
                  interest expenses to be less than the following amounts for
                  the following periods: (i) 0.75 to 1.0 for the four quarters
                  ending June 30, 2000; (ii) 0.85 to 1.0 for the four quarters
                  ending September 30, 2000; and (iii) 2.5 to 1.0 for the four
                  quarters ending December 31, 2000 and on each March 31, June
                  30, September 30 and December 31 thereafter on a rolling four
                  quarter basis.

         2.8      Section 7.9 of the Loan Agreement is amended to provide as
                  follows:

                  7.9 FUNDED DEBT TO EBITDA. Permit the ratio of Consolidated
                  Funded Debt to consolidated earnings before interest, taxes,
                  depreciation and amortization and excluding any gains from
                  sales of assets, other non-cash gains and extra-ordinary gains
                  ("EBITDA"), to exceed the following amounts for the following
                  periods: (i) 3.5 to 1.0 for the four quarters ending June 30,
                  2000; (ii) 3.25 to 1.0 for the four quarters ending September
                  30, 2000, and (iii) 3.0 to 1.0 for the four quarters ending
                  December 31, 2000 and as measured on each March 31, June 30,
                  September 30 and December 31 on a rolling four quarter basis.

         2.9      The Loan Agreement is amended to add a new Section 7.18 that
                  provides as follows:

                  7.18 NOTE PURCHASE AGREEMENT. Permit Borrower to take any
                  action under this Agreement that could or would with the
                  passage of time result in the


                                       2
<PAGE>   3

                  occurrence of a default or an Event of Default under the Note
                  Purchase Agreement dated as of May 30, 1997.

         2.10     The Loan Agreement is amended to add a new sentence at the end
                  of Section 14.13 that provides as follows: "For the purposes
                  of any future date on which the representations and warranties
                  contained in SECTION 5 hereof are deemed to be remade, the
                  most current financial statements, tax returns or other
                  documents with respect to Borrower or any Guarantor delivered
                  to Lender pursuant to SECTION 6 above will be deemed the
                  "Current Financial Statements"."

         2.11     The Loan Agreement is amended to add a new Section 14.13A,
                  which provides as follows:

                  14.13A "Debt" will mean, without duplication: (i) all
                  obligations (including capitalized lease obligations) which in
                  accordance with generally accepted accounting principles would
                  be shown on a balance sheet as a liability; (ii) all
                  obligations for borrowed money or for the deferred purchase
                  price of property or services; (iii) all guarantees,
                  reimbursement, payment or similar obligations, absolute,
                  contingent or otherwise, under acceptance, letter of credit or
                  similar facilities, and (iv) all obligations for any Swap. For
                  the purposes of this Section, "Swap" shall mean, with respect
                  to any Person, payment obligations with respect to interest
                  rate swaps, currency swaps, and similar obligations obligating
                  such Person making payments, whether periodically or upon the
                  happening of a contingency. The amount of the obligation under
                  any Swap shall be the amount determined by Lender in its
                  reasonable calculation to be that portion of the Swap
                  obligation that represents the credit risk of such Person
                  under the Swap.

         2.12     Section 14.25 of the Loan Agreement is hereby amended to
                  provide as follows:

                  14.25 "Indebtedness" will mean, without duplication: (i) all
                  obligations for borrowed money or for the deferred purchase
                  price of property (including capitalized lease obligations) or
                  services; (ii) all guarantees, reimbursement, payment or
                  similar obligations, absolute, contingent or otherwise, under
                  acceptance, letter of credit or similar facilities, and (iii)
                  all obligations for any Swap. For the purposes of this
                  Section, "Swap" shall mean, with respect to any Person,
                  payment obligations with respect to interest rate swaps,
                  currency swaps, and similar obligations obligating such Person
                  making payments, whether periodically or upon the happening of
                  a contingency. The amount of the obligation under any Swap
                  shall be the amount determined by Lender in its reasonable
                  calculation to be that portion of the Swap obligation that
                  represents the credit risk of such Person under the Swap.

         2.13     Section 14.39 of the Loan Agreement is hereby amended to
                  provide as follows:

                  14.39 "Prime Rate" means the higher of: (i) that interest rate
                  established from time to time by Lender as Lender's Prime
                  Rate, whether or not such rate is publicly announced, or (ii)
                  one half of one percent (0.5%) plus the Federal


                                       3
<PAGE>   4

                  Funds Effective Rate. The Prime Rate may not be the lowest
                  interest rate charged by Lender for commercial or other
                  extensions of credit. As used herein, the "Federal Funds
                  Effective Rate" will mean a fluctuating interest rate per
                  annum equal for each day during such period to the weighted
                  average of the rates on overnight Federal funds transactions
                  with members of the Federal Reserve System arranged by Federal
                  funds brokers, as published for the prior day (or, if such day
                  is not a Business Day, for the next preceding Business Day) by
                  the Federal Reserve Bank of New York, or, if such rate is not
                  so published for any day that is a Business Day, the average
                  of the opening quotations for such day for such transactions
                  received by Lender from three Federal funds brokers of
                  recognized standing selected by it.

         2.14     Add a new Section 14.40A to the Loan Agreement that provides
                  as follows:

                  14.40A "Proxy Statement/Prospectus" will mean any document for
                  disclosure or reporting purposes filed with the Securities and
                  Exchange Commission and publicly available.

3.       REPRESENTATIONS  AND WARRANTIES.  To induce Lender to enter into this
         Amendment,  Borrower  represents and warrants as follows:

         3.1      The representations and warranties of Borrower contained in
                  Section 5 of the Loan Agreement are deemed to have been made
                  again on and as of the date of execution of this Amendment and
                  will apply to this Amendment; provided that Lender
                  acknowledges that Borrower has unusual and extraordinary
                  expenses for which it has no reserve resulting from the failed
                  Blackstone transaction and the resulting plans of Borrower to
                  divide Borrower's business.

         3.2      No Event of Default (as such term is defined in Section 8 of
                  the Loan Agreement) or event or condition which with the lapse
                  of time or giving of notice or both would constitute an Event
                  of Default exists on the date hereof.

         3.3      Each person executing this Amendment and the loan documents to
                  be executed in connection herewith is a duly elected and
                  acting officer of Borrower and is duly authorized by the Board
                  of Directors of Borrower to execute and deliver such documents
                  on behalf of Borrower.

4.       CONDITIONS. Lender's consent to this Amendment is subject to the
         following conditions:

         4.1      Borrower will have provided Lender with consolidating
                  statements of Borrower and each of Borrower's subsidiaries
                  that are required to be consolidated with Borrower according
                  to generally accepted accounting principles.

         4.2      Borrower will have executed and delivered to Lender the
                  Amendment to the Revolving Credit Note.



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<PAGE>   5

         4.3      Lender will have been furnished copies, certified by the
                  Secretary or Assistant Secretary of Borrower, of resolutions
                  of the Board of Directors of Borrower authorizing the
                  execution of this Amendment and all other documents executed
                  in connection herewith.

         4.4      The representations and warranties of Borrower in SECTION 3
                  herein will be true.

         4.5      Borrower will pay to Lender a facility fee of $125,000 for the
                  increase, and $100,000 fee for waiving certain covenant
                  violations.

         4.6      Borrower shall pay all expenses and attorneys' fees incurred
                  by Lender in connection with the preparation, execution, and
                  delivery of this Amendment in the amount of $1,750, and
                  related documents, including but not limited to outstanding
                  legal bills for other matters, which outstanding legal bills
                  total $7,574.80, for a combined total of $9,324.80. Borrower
                  hereby authorizes Lender to pay these sums by making an
                  advance under the Revolving Credit Note.

5.       GENERAL.

         5.1      Except as expressly modified herein, the Loan Agreement, as
                  amended, and the Revolving Credit Note, as amended, are and
                  remain in full force and effect.

         5.2      Nothing contained herein will be construed as waiving any
                  default or Event of Default under the Loan Agreement or will
                  affect or impair any right, power or remedy of Lender under or
                  with respect to the Loan, the Loan Agreement, as amended, the
                  Revolving Credit Note, as amended, or any agreement or
                  instrument guaranteeing, securing or otherwise relating to the
                  Loan.

         5.3      This Amendment will be binding upon and inure to the benefit
                  of Borrower and Lender and their respective successors and
                  assigns.

         5.4      All representations, warranties and covenants made by Borrower
                  herein will survive the execution and delivery of this
                  Amendment.

         5.5      This Amendment will in all respects be governed and construed
                  in accordance with the laws of the State of Ohio.




                            [SIGNATURES ON NEXT PAGE]


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<PAGE>   6


         Signed on May     , 2000.
                       ----


                                           THE KROLL-O'GARA COMPANY


                                           By:
                                               ---------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------


                                           O'GARA-HESS & EISENHARDT
                                           ARMORING COMPANY


                                           By:
                                               ---------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------

                                           KROLL HOLDINGS, INC.


                                           By:
                                               ---------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------

                                           KROLL ASSOCIATES, INC.


                                           By:
                                               ---------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------

                                           KEYBANK NATIONAL ASSOCIATION

                                           By:
                                               ---------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------




<PAGE>   7


                       AMENDMENT TO REVOLVING CREDIT NOTE

Cincinnati, Ohio                                        Dated as of May __, 2000

         On June 25, 1999, the undersigned, THE KROLL-O'GARA COMPANY, O'GARA -
HESS & EISENHARDT ARMORING COMPANY, KROLL HOLDINGS, INC., and KROLL ASSOCIATES,
INC. (individually and collectively the "Borrower"), executed and delivered a
Revolving Credit Note to KEYBANK NATIONAL ASSOCIATION, in the principal amount
of $25,000,000 (the "Note").

         By this Amendment to Revolving Credit Note, the Note hereby is amended
as follows:1. The first full paragraph on the first page of the Note is amended
to provide as follows:

                           FOR VALUE RECEIVED, THE KROLL-O'GARA COMPANY, O'GARA
                  - HESS & EISENHARDT ARMORING COMPANY, KROLL HOLDINGS, INC.,
                  and KROLL ASSOCIATES, INC. (individually and collectively the
                  "Borrower"), jointly and severally promise to pay to the order
                  of KEYBANK NATIONAL ASSOCIATION ("Lender"), at its offices
                  located at 525 Vine Street, Cincinnati, Ohio 45202 or such
                  other location as Lender may from time to time designate, the
                  principal sum of TWENTY FIVE MILLION DOLLARS ($25,000,000)
                  (the "Total Facility") or such greater or lesser amount as may
                  be advanced and outstanding hereunder, together with interest
                  thereon as provided below from the date of disbursement
                  thereof until paid, all in lawful money of the United States
                  of America and in immediately available funds. Notwithstanding
                  any of the foregoing to the contrary, the Total Facility will
                  be increased from $25,000,000 to $40,000,000 until September
                  30, 2000 (the "Reduction Date"), at which time it will reduce
                  from $40,000,000 to $25,000,000, and Borrower will pay to
                  Lender on the Reduction Date the principal balance outstanding
                  hereunder that is in excess of $25,000,000.

2.       The following sentence will be added to the end of Section 1.1.2 of
         the Note as follows:

         Notwithstanding any of the foregoing to the contrary, on May __, 2000,
         the Applicable Margin will be set as if Borrower's Funded Debt to
         EBITDA Ratio is greater than or equal to 2.5 to 1.0, which Applicable
         Margin will apply until the Reduction Date.

         Except as expressly modified hereby, all terms and conditions of the
Note remain in full force and effect.

                                           THE KROLL-O'GARA COMPANY


                                           By:
                                              ----------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------



                                       7
<PAGE>   8

                                           O'GARA-HESS & EISENHARDT
                                           ARMORING COMPANY


                                           By:
                                              ----------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------

                                           KROLL HOLDINGS, INC.


                                           By:
                                              ----------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------

                                           KROLL ASSOCIATES, INC.


                                           By:
                                              ----------------------------------
                                           Print Name:
                                                      --------------------------
                                           Title:
                                                 -------------------------------
                                           Date:
                                                --------------------------------

ACCEPTED:
KEYBANK NATIONAL ASSOCIATION

By:
   ----------------------------
Print Name:
           --------------------
Title:
      -------------------------
Date:
      -------------------------







                                       8
<PAGE>   9


                          CERTIFICATE OF THE SECRETARY

                                       OF

                            THE KROLL-O'GARA COMPANY

         The undersigned, Secretary of THE KROLL-O'GARA COMPANY ("Corporation")
hereby certifies to KEYBANK NATIONAL ASSOCIATION ("Lender") as follows:

1.       The following Resolution was duly adopted and is a binding resolution
         of the Corporation:

                  RESOLVED, that the Corporation amend the Amended and Restated
         Loan Agreement by and between Corporation, O'Gara-Hess & Eisenhardt
         Armoring Company, Kroll Holdings, Inc. and Kroll Associates, Inc.
         (collectively, "Borrowers") and Lender dated October 30, 1998, as
         amended, and the Revolving Credit Note (the "Note") given by Borrowers
         to Lender on June 25, 1999, to extend the maturity date of the letter
         of credit facility, to increase the amount of the Note until September
         30, 2000, and to amend certain other financial provisions, and that the
         President or any Vice President be, and they hereby are, authorized to
         execute any and all documents to effectuate and secure such loan
         including, without limitation, a Third Amendment to Loan Agreement, an
         Amendment to Revolving Credit Note and other necessary or appropriate
         documents in connection herewith.

2.       The following is a complete and accurate list of the Officers of the
         Corporation as of May __, 2000:

                  President.................
                                                --------------------------

                  Vice President............
                                                --------------------------

                  Secretary.................
                                                --------------------------

                  Assistant Secretary.......
                                                --------------------------

                  Treasurer.................
                                                --------------------------




                                                --------------------------
                                                Secretary



                                       9
<PAGE>   10

                          CERTIFICATE OF THE SECRETARY

                                       OF

                    O'GARA-HESS & EISENHARDT ARMORING COMPANY

         The undersigned, Secretary of O'GARA-HESS & EISENHARDT ARMORING COMPANY
("Corporation") hereby certifies to KEYBANK NATIONAL ASSOCIATION ("Lender") as
follows:

1.       The following Resolution was duly adopted and is a binding resolution
         of the Corporation:

                  RESOLVED, that the Corporation amend the Amended and Restated
         Loan Agreement by and between Corporation, The Kroll-O'Gara Company,
         Kroll Holdings, Inc. and Kroll Associates, Inc. (collectively,
         "Borrowers") and Lender dated October 30, 1998, as amended, and the
         Revolving Credit Note (the "Note") given by Borrowers to Lender on June
         25, 1999, to extend the maturity date of the letter of credit facility,
         to increase the amount of the Note until September 30, 2000, and to
         amend certain other financial provisions, and that the President or any
         Vice President be, and they hereby are, authorized to execute any and
         all documents to effectuate and secure such loan including, without
         limitation, a Third Amendment to Loan Agreement, an Amendment to
         Revolving Credit Note and other necessary or appropriate documents in
         connection herewith.

2.       The following is a complete and accurate list of the Officers of the
         Corporation as of May __, 2000:

                  President.................
                                                --------------------------

                  Vice President............
                                                --------------------------

                  Secretary.................
                                                --------------------------

                  Assistant Secretary.......
                                                --------------------------

                  Treasurer.................
                                                --------------------------



                                                --------------------------
                                                Secretary








                                       10
<PAGE>   11


                          CERTIFICATE OF THE SECRETARY

                                       OF

                              KROLL HOLDINGS, INC.

         The undersigned, Secretary of KROLL HOLDINGS, INC. ("Corporation")
hereby certifies to KEYBANK NATIONAL ASSOCIATION ("Lender") as follows:

1.       The following Resolution was duly adopted and is a binding resolution
         of the Corporation:

                  RESOLVED, that the Corporation amend the Amended and Restated
         Loan Agreement by and between Corporation, O'Gara-Hess & Eisenhardt
         Armoring Company, The Kroll-O'Gara Company and Kroll Associates, Inc.
         (collectively, "Borrowers") and Lender dated October 30, 1998, as
         amended, and the Revolving Credit Note (the "Note") given by Borrowers
         to Lender on June 25, 1999, to extend the maturity date of the letter
         of credit facility, to increase the amount of the Note until September
         30, 2000, and to amend certain other financial provisions, and that the
         President or any Vice President be, and they hereby are, authorized to
         execute any and all documents to effectuate and secure such loan
         including, without limitation, a Third Amendment to Loan Agreement, an
         Amendment to Revolving Credit Note and other necessary or appropriate
         documents in connection herewith.

2.       The following is a complete and accurate list of the Officers of the
         Corporation as of May __, 2000:

                  President.................
                                                --------------------------

                  Vice President............
                                                --------------------------

                  Secretary.................
                                                --------------------------

                  Assistant Secretary.......
                                                --------------------------

                  Treasurer.................
                                                --------------------------



                                                --------------------------
                                                Secretary



                                       11
<PAGE>   12


                          CERTIFICATE OF THE SECRETARY

                                       OF

                             KROLL ASSOCIATES, INC.

         The undersigned, Secretary of KROLL ASSOCIATES, INC. ("Corporation")
hereby certifies to KEYBANK NATIONAL ASSOCIATION ("Lender") as follows:

1.       The following Resolution was duly adopted and is a binding resolution
         of the Corporation:

                  RESOLVED, that the Corporation amend the Amended and Restated
         Loan Agreement by and between Corporation, O'Gara-Hess & Eisenhardt
         Armoring Company, Kroll Holdings, Inc. and The Kroll-O'Gara Company
         (collectively, "Borrowers") and Lender dated October 30, 1998, as
         amended, and the Revolving Credit Note (the "Note") given by Borrowers
         to Lender on June 25, 1999, to extend the maturity date of the letter
         of credit facility, to increase the amount of the Note until September
         30, 2000, and to amend certain other financial provisions, and that the
         President or any Vice President be, and they hereby are, authorized to
         execute any and all documents to effectuate and secure such loan
         including, without limitation, a Third Amendment to Loan Agreement, an
         Amendment to Revolving Credit Note and other necessary or appropriate
         documents in connection herewith.

3.       The following is a complete and accurate list of the Officers of the
         Corporation as of May __, 2000:

                  President.................
                                                --------------------------

                  Vice President............
                                                --------------------------

                  Secretary.................
                                                --------------------------

                  Assistant Secretary.......
                                                --------------------------

                  Treasurer.................
                                                --------------------------



                                                --------------------------
                                                Secretary