<PAGE>   1
                                                                   EXHIBIT 10.24


                              SUBLEASE AGREEMENT


        THIS SUBLEASE AGREEMENT (the "Sublease"), dated as of 4-22-97, 
is entered into by and between America Service Group Inc. as the
Sublandlord ("Sublandlord") and Citibank Delaware as the subtenant
("Subtenant").  Commons Development Group ("Prime Landlord") joins in this
Sublease Agreement pursuant to the terms hereof.

                                  WITNESSETH


        WHEREAS, by an Office Lease Agreement dated June 23, 1994 (the "Primary
Lease") Sublandlord now leases from Prime Sublandlord certain Premises (the
"Leased Premises") at 2 Penns Way, New Castle, Delaware, 19720 (the
"Building").  A portion of the Leased Premises includes the premises being
subleased hereunder, 21,000 square feet on the second floor of the Building,
Suite 200, (the "Subleased Premises").

        WHEREAS, Sublandlord is willing to sublease to Subtenant and Subtenant
is willing to sublease from Sublandlord the Subleased Premises, as more fully
described herein, on the terms and conditions set forth herein.

        NOW THEREFORE, Prime Landlord, Sublandlord and Subtenant agree as
follows:

        1.  SUBLEASED PREMISES.  Sublandlord hereby subleases to Subtenant and
Subtenant hereby subleases 21,000 square feet of the Leased Premises, located
on the second floor of 2 Penns Way, New Castle, Delaware, such subleased space
shown on Exhibit "A" attached hereto.

        2.  TERM.  The term of Sublease will be for a period of 24 months,
commencing on May 1, 1997 and terminating on April 30, 1999.  Provided
Subtenant is not in default in any of the terms and conditions of this Sublease
Agreement, Sublandlord hereby grants the Subtenant two (2) option periods (the
"Option Period") of 6 months, the first option period commencing on May 1, 1999
and the second option period commencing November 1, 1999 to extend this
Sublease as between Subtenant, Sublandlord, and Prime Landlord.  Subtenant must
give Sublandlord and Prime Landlord written notice prior to the commencement of
the option periods of its intention to exercise said option; said notice to be
given on or before November 1, 1998 with respect to the First Option Period and
May 1, 1999 with respect to the Second Option Period.  In order for the Option
Periods to apply, Subtenant must also not be in breach of any obligation under
this Sublease to Sublandlord and Prime Landlord both at the time Subtenant
gives written notice of its intention to exercise the option herein granted and
on May 1, 1999, or November 1, 1999, when the Option Period begins. 
Sublandlord agrees that it shall give Subtenant a reminder notice with regard
to each applicable option no earlier than August 1, 1998 for the first Option
Period and no earlier than February 1, 1999 for the second Option Period and
the period within which Subtenant
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shall be required to exercise each applicable option shall be as set forth
above or thirty (30) days after Sublandlord's reminder notice, whichever is
later.

           3.  USE.  During the term hereof, Subtenant shall use and occupy the
Subleased Premises for general office use, and for any other use permitted
under the Primary Lease and complying with all local building and zoning laws.

           4.  RENTAL RATE.  As rental for the Subleased Premises, Subtenant 
shall pay monthly base rental to Prime Landlord, during the Sublease term and 
any option period, based on the following rental schedule:

<TABLE>
<CAPTION>
                        Term                   Monthly Base Rent
                        ----                   -----------------
                <S>                               <C>
                05/01/97 - 04/30/99               $27,125.00

</TABLE>


           If exercised, Subtenant shall pay monthly base rental to Prime 
Landlord, during the term of the Option Periods, at a rate of $28,000.00 per 
month.

           Rents will be due and payable in advance of the first day of each 
month during the term hereof.  In the event this Sublease commences or 
terminates on other than the first day of any particular month, all rents 
hereunder shall be prorated.

        5. OPERATING EXPENSES.  Subtenant shall pay to Prime Landlord, as
additional rent, its electric usage during the Sublease term and any extension
thereof.  Prime Landlord will read submeter monthly and bill Subtenant according
to the average kilowatt hour charge per month for the building.  Subtenant
shall have no obligation to pay any other operating expenses or real estate
taxes with respect to the Subleased Premises.

        6. IMPROVEMENTS.  It is understood and agreed that the Subtenant will 
accept the Premises in "as-is" condition.  Sublandlord shall provide the 
Premises to Subtenant on April 1, 1997 for commencement of Subtenant 
Improvement work.  All plans and specifications must be approved by Prime 
Landlord prior to construction.  No rent will be due during this period April 
1, 1997 - April 30, 1997.

        7. SECURITY DEPOSIT.

           Intentionally omitted.

        8. PRIMARY LEASE INCORPORATION.  Subtenant acknowledges and agrees that
this Sublease shall be in all respects subject and subordinate to the Primary 
Lease.  In the event that the Primary Lease is canceled or terminated for any 
reason, the term of this Sublease shall automatically terminate simultaneously
therewith subject, however to the provisions of Paragraph


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convenient for the maintenance and operation thereof and including to show the
space to other prospective subtenants.  Sublandlord shall comply while in
Subleased Premises with all reasonable safety and security measures instituted
by Subtenant all in a manner such as not to unreasonably interfere with
Subtenants's operation.

        10.  COMPLIANCE WITH LAW.  Subtenant shall comply with all applicable
statutes, ordinances, rules, regulations, orders and directives of any
governmental authority specifically applicable to Subtenant's use or occupancy
thereof and shall perform, at its own expense, all obligations imposed
thereby.

        11.  RELEASE AND INDEMNITY.

             Intentionally Omitted.

        12.  INSURANCE.

             Notwithstanding any provision contained herein or in the Primary
Lease to the contrary, all insurance for which Subtenant is responsible
hereunder may include or consist entirely of alternative risk management
programs, including self insurance, for so long as Subtenant or its affiliates,
parent or subsidiary is the tenant hereunder.

        13.  DEFAULTS.  The occurrence of any of the following shall constitute
a default by Subtenant under this Sublease:

             (a)  Subtenant fails to pay any sum as required hereunder and such
failure continues for ten (10) days following receipt of notice;

             (b)  Subtenant becomes insolvent or makes transfers in fraud of
creditors or makes any assignment for the benefit of creditors; or (iii) files
a petition for protection under any state or federal bankruptcy act or a
trustee or receiver is appointed for all or substantially all of Subtenant's
assets, and with regard to any of the foregoing, Subtenant fails to cure any of
the foregoing within thirty (30) days after Subtenant's receipt of written
notice of such default from Sublandlord or Prime Landlord.

        14. REMEDIES UPON DEFAULT.
        
        (A) Upon the occurrence of any of the aforesaid Events of Default,
Sublandlord shall:

            (I)  serve upon Subtenant a written notice that this Sublease and 
the Term will terminate on a date to be specified therein, which shall not be 
less than three days after the giving of such notice, and upon the date so
specified therein, this Sublease and the Term shall terminate and come to an
end as fully and completely as if such date were the date herein definitely
fixed for the end and expiration of this Sublease and the Term, and Subtenant 
shall then quit and

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surrender the Premises to Sublandlord, but Subtenant shall nevertheless remain
liable as hereinafter set forth.  If the notice above provided legal shall have
been given and this Sublease shall be terminated, Sublandlord may, without
notice, re-enter the Premises either by legal process or by summary proceedings
or otherwise, dispossess Subtenant and the legal representative of Subtenant or
other occupant of the Premises as if this Sublease had not been made.

     (ii)  Without terminating this Sublease, Sublandlord may re-enter or take
possession pursuant to legal proceedings or pursuant to any notice provided by
law and, may, from time to time, without terminating this Sublease, relet the
Premises or any part thereof in Sublandlord's or Subtenant's name, for such
term or terms (which may be greater or less than the period which would
otherwise have constituted the balance of the Term) and on such terms and
conditions as Sublandlord, in its sole discretion, may determine, and
Sublandlord may collect and receive the rents therefor without relieving
Subtenant of any liability under this Sublease or otherwise affecting any such
liability.  Sublandlord shall have no obligation to relet the Premises or any
part thereof, but shall use reasonable efforts to do so.  No such re-entry or
taking possession of the Premises by Sublandlord shall be construed as an
election on Sublandlord's part to terminate this Sublease unless a written
notice of such intention be given to subtenant.  No notice from Sublandlord
hereunder or under a forcible entry and detainer statute or similar law shall
constitute an election by Sublandlord to terminate this Sublease unless such
notice specifically so states.  Sublandlord reserves the right following any
such re-entry and/or reletting to exercise its right to terminate this Sublease
by giving Subtenant written notice thereof, in which event this Sublease will
terminate as specified in said notice.

     (iii)  enter upon the demised Premises by legal process, if necessary,
without being liable for prosecution or any claim of damages therefor, and do
whatever Subtenant is obligated to do under the terms of this Sublease, and
Subtenant agrees to reimburse Sublandlord on demand for any expenses including,
without limitation, reasonable attorney's fees which Sublandlord may incur in
thus effecting compliance with Subtenant's obligations under this Sublease and
Subtenant further agrees that Sublandlord shall not be liable for any damages
resulting to Subtenant from such action, whether caused by negligence of
Sublandlord or otherwise; or

  (b)  If this Sublease and the Term shall expire and come to an end as provided
in this Agreement, or by or under any summary proceeding or any other action or
proceeding; or if Sublandlord shall re-enter the Premises as provided in Section
(b)(ii), or by or under any summary proceeding or any other action or
proceeding, then, in any of said events:

        (I)  Subtenant shall pay Sublandlord all Rent payable under this 
Sublease by Subtenant to Sublandlord to the date upon which date this Sublease 
and the Term shall have expired and come to an end or to the date of re-entry 
upon the Premises by Sublandlord, as the case may be;

        (ii)  Subtenant also shall be liable for and shall pay to Sublandlord,
as damages, any deficiency (the "Deficiency") between the Rent for the period
which otherwise would have

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constituted the unexpired portion of the Term and the net amount, if any, of
rents collected in respect of any reletting effected pursuant to the provisions
of Section (b)(ii) for such period, together with all of Sublandlord's expenses
in connection with the termination of this Sublease with Sublandlord's re-entry
upon the Premises and with such reletting including, but not limited to, all
possession costs, brokerage commissions, legal expenses, attorney's fees and
disbursements, alteration costs and other expenses of preparing the Premises
for such reletting.  Subtenant shall pay Sublandlord these costs as and when
such expenses are incurred by Sublandlord.  Any such Deficiency shall be paid
in monthly installments by Subtenant on the days specified in this Sublease for
payment of installments of Rent.  Sublandlord shall be entitled to recover from
Subtenant each monthly Deficiency as the same shall arise, and no suit to
collect the amount of the Deficiency for any month shall prejudice
Sublandlord's right to collect the Deficiency for any subsequent month by a
similar proceeding; and

        (iii)  Whether or not Sublandlord shall have collected any monthly
Deficiencies as aforesaid, Sublandlord shall be entitled to recover from
Subtenant, and Subtenant shall pay Sublandlord, on demand, in lieu of any
further Deficiencies, as and for liquidated and agreed final damages, a sum
equal to the amount of the Rent for the period which otherwise would have
constituted the unexpired portion of the Term discounted at the prime rate then
announced by Citibank, Delaware.

   (c)  Pursuit of any of the foregoing remedies shall not preclude pursuit of 
any other remedy herein provided or any other remedy herein provided constitute
an election of remedies thereby excluding the later election of any alternate
remedy, or a forfeiture or waiver of any Gross Base Rent, additional rent or
other charges and assessment payable by Subtenant and due to Sublandlord
hereunder or of any damages accruing to Sublandlord by reason of violation of
any of the terms, covenants, warranties and provisions herein contained.  No
action taken by or on behalf of Sublandlord shall be construed to be an
acceptance of a surrender of this Sublease.  Forbearance by Sublandlord to
enforce one or more of the remedies herein provided upon an event of default
shall not be deemed or construed to constitute a waiver of such default.  In
determining the amount of loss or damage which Sublandlord may suffer by reason
of termination of this Sublease or the deficiency arising by reason of any
reletting of the Premises by Sublandlord as above provided, allowance shall be
made for expense of repossession and the Gross Base Rent and additional rent
herein provided, for the period from the time of an event of default until the
end of the term hereof, shall be deemed to be equal to the highest Base Rent
and additional rent required to be paid hereunder by Subtenant during any
preceding lease year multiplied by the number of calendar years or portions
thereof remaining in the term hereof.  Subtenant agrees to pay to Sublandlord
all costs and expenses incurred by Sublandlord in the enforcement of this
Sublease, including without limitation, the reasonable fees of Sublandlord's
attorneys when such attorneys are employed by Sublandlord to effect collection
of any sums due hereunder or to enforce any right or remedy of Sublandlord.

   15.  CUMULATIVE RIGHTS.  Sublandlord's and Prime Landlord's rights and 
remedies hereunder shall be cumulative and shall not be exclusive of one
another, and Sublandlord and

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Prime Landlord shall have the right to pursue any one or more of them. 
Sublandlord's or Prime Landlord's acceptance of any rent or other payments due
hereunder or Sublandlord's or Prime Landlord's failure to take any action on
account of default if such default persists requiring Sublandlord's or Prime
Landlord's consent or approval shall not be deemed to waive or render
unnecessary Sublandlord's or Prime Landlord's consent or approval to any
subsequent or similar acts by Subtenant.

        16.  SURRENDER OF SUBLEASED PREMISES/HOLDING OVER.  At the expiration
or earlier termination of this Sublease, Subtenant shall surrender the
Subleased Premises to Sublandlord or Prime Landlord in good conditions, broom
clean, reasonable wear and tear, condemnation and casualty excepted.  In the
event that Subtenant remains in possession after the expiration of or
termination of this Sublease without a written agreement, or without Subtenant
being engaged in active negotiations with Prime Landlord or Sublandlord in good
faith to renew or extend the term, the tenancy shall be deemed to be a
month-to-month tenancy at a monthly rent equal to one and one-half (1 1/2)
times the sum of the Base Rent payable during the last month of the Term. 
Notwithstanding any provision of the Primary Lease or this Sublease, Subtenant
shall not have any obligation to remove any tenant improvement existing on the
date hereof or made by Subtenant with the consent of Prime Landlord during the
term of the Sublease.

        17.  ASSIGNMENT AND SUBLEASE.  Subtenant shall not assign this Sublease
or any right hereunder or sublet the Subleased Premises during the term of this
Sublease, without the prior written consent of Sublandlord and Prime Landlord,
such consent not to be unreasonably withheld, delayed or denied.  In the event
of an assignment or sublease, Sublandlord during the original term of this
Sublease or Prime Landlord during the Option Period, shall be entitled to
receive fifty percent (50%) of the excess of the rent and other sums payable to
the Subtenant under such Sublease over the amount of Rent payable hereunder for
the Sublease space.  Sublandlord's or Prime Landlord's acceptance of rent from
any person other than Subtenant shall not be deemed to be a waiver of this
provision.  Consent to one assignment or subletting shall not be deemed to be
consent to any subsequent assignment or subletting.  Notwithstanding any
provision contained herein or in the Primary Lease to the contrary, none of (1)
an assignment or subletting of all or a portion of the Subleased Premises to a
parent, subsidiary or affiliate of Subtenant or Subtenant's parent
(collectively, an "Affiliate") or to a purchaser of all or substantially all of
the assets of Subtenant or any Affiliate, (ii) a transfer, by operation of law
or otherwise, in connection with the merger, consolidation or other
reorganization of Subtenant or any Affiliate, (iii) or the use or occupancy of
portions of the Subleased Premises by an Affiliate, or by a party or parties in
connection with the transaction of business with Subtenant or any Affiliate on
a temporary basis, shall require the prior written consent of Sublandlord or
Prime Landlord.

        18.  ACCORD AND SATISFACTION.  No payment or receipt by Sublandlord or
Prime Landlord of a lesser amount than the rent or other charges herein
stipulated shall be deemed to be other than on account of the rent or such
charges.  Further, no endorsement or statement on any check or any letter
accompanying any check shall be deemed to be an accord and satisfaction. 
Sublandlord or Prime Landlord may accept such check or payment without
prejudice to

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Sublandlord's or Prime Landlord's right to recover the balance of such rent or
other charges or pursue any other remedy provided in this Sublease.

        19.  ENTIRE AGREEMENT.  This Sublease constitutes the complete
agreement of the parties with respect to the subject matter hereof and
supersedes all previous agreements, representation and undertakings concerning
the same, whether written or oral.  The provisions of the Sublease may be
modified, amended or waived only by a written instrument executed by
Sublandlord, Prime Landlord and Subtenant.

        20.  PRIME LANDLORD'S NON-DISTURBANCE AGREEMENT.  In the event of any
termination of the Prime Lease Prior to the expiration of its term, including
without limitation, any termination by reason of rejection of the Prime Lease
or other action by a trustee, court or debtor in possession pursuant to the
Federal Bankruptcy Code, as amended, or any other Federal, state or local
insolvency laws, effective as of the date of termination of the Prime Lease,
Subtenant shall be deemed attorned to the Prime Landlord and Subtenant shall
become a tenant of the Prime Landlord under this Sublease and the Prime
Landlord (as landlord) shall be bound to Subtenant under all of the covenants,
agreements, terms, provisions and limitations (including any options to renew)
of the Sublease; provided, however, upon the written request of the Subtenant,
the Prime Landlord shall enter into a new lease of the Subleased Premises with
the Subtenant for the remainder of the term of the Sublease, effective as of
the date of termination of Prime Lease, on the same covenants, agreements,
terms, provisions and limitations (including any options to renew) as the
Sublease.

        21.  NOTICES.  Any notice required or sent hereunder shall be in
writing and shall be sent as follows:
 
                        To:  Sublandlord
                             America Service Group, Inc.
                             Attention:  General Counsel
                             Suite 300
                             105 West Park Drive
                             Brentwood, TN  37027

                        To:  Subtenant
                             Citicorp North America, Inc.
                             Corporate Realty Services
                             12401 Prosperity Drive
                             Silver Spring, MD  20904
                             Attention:  Simon Key


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           with a copy to:      
           Citi Bank Delaware    
           1 Penns Way          
           New Castle, DE  19720
           Attention:  Ben Walsh

Copies of any notices commencing or relating to any action, suite or proceeding
against Subtenant arising hereunder shall also be sent to:


           Citicorp/Citibank Real Estate and Infrastructure Legal Division
           Attention:  General Counsel
           599 Lexington Avenue
           24th Floor, Zone 9
           New York, NY  10043

           with a copy to:
           Weil, Gotshal & Manges LLP
           701 Brickell Avenue, Suite 2100
           Miami, FL  33131
           Attention:  Barry Frank
                   
Invoice or insurance requests shall be sent in writing to:

           Citicorp North America
           201 S. Biscayne Blvd., 5th Floor
           Miami, FL  33131
           Attention:  Lease Administrator

      To:  Prime Landlord
           Commons Development Group
           c/o Emory Hill Management Company, Inc.
           92 Read's Way, Suite 100
           New Castle, DE  19720

      Either party from time to time, may change its address by written notice
to the other party.  Notices hereunder shall be deemed effective when delivered
by hand delivery or overnight courier, or three days after deposit in the
United States mail, first class, postage prepaid.

22.  BINDING EFFECT.  Subject to prohibitions against assignment, this Sublease
shall be binding upon the parties their personal representatives, successors
and assigns.


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        23.  APPROVALS.  Whenever in this Sublease, the written approval of
either Sublandlord or Subtenant is required, the parties hereto agree that such
approval shall not be unreasonably withheld.

        24.  ADDITIONAL PROVISIONS.

             A.  Signage.

                    Subtenant may have an interior Building Standard tenant 
plaque and a listing on the interior tenant directory, which shall be ordered, 
paid for, provided and mounted by Sublandlord in such a manner as to be 
consistent with the Building Standards.  

             B.  Nondisturbance.

                    Subtenant will agree to not require a Non-Disturbance 
Agreement as part of this Sublease Agreement from any fee Mortgagee.

             C.  Consent

                    Whenever the approval of Sublandlord shall be required with
respect to any matter under this Sublease, such approval shall be deemed given
if the Prime Landlord has given its approval with respect to such matter.

             D.  Parking.

                    Subtenant agrees to accept the existing parking ratio in 
the building which is 3.3 space per 1,000 square feet of rentable area.

             E.  Brokerage

                    Unless otherwise disclosed, broker, any cooperating broker,
and any salesperson working with either, are representing the Sublandlord's 
interest and have fiduciary responsibilities to Sublandlord, but are obligated 
to treat all parties fairly.  Broker, any cooperating broker, and any 
salesperson working either, without breaching the fiduciary responsibilities 
to lessor, may, among other services, provide a potential tenant with 
information about the attributes of properties and available financing, show 
properties, and assist in preparing an offer to lease.  Broker, any cooperating
broker, and any salesperson working with either, also have the duty to respond 
accurately and honestly to a potential tenant's questions and disclose material
facts about properties, submit promptly any offers to lease and offer 
properties without unlawful discrimination.

                    Except for Commonwealth Emory Hill Development Company, Inc.
("Broker"), Subtenant and Sublandlord represent that they have dealt only with
each other in connection with this 

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Sublease Agreement and that no other broker negotiated this Sublease Agreement
or is entitled to any commission in connection with it.  Sublandlord shall
compensate Broker under the terms of separate agreement between Sublandlord and
Broker and shall hold Subtenant harmless from liability to Broker in connection
with this Sublease Agreement.

                F.  Elevator.

                      Prime Landlord agrees that at least one passenger 
elevator shall be maintained in operation for Subtenant's use twenty-four hours
a day, seven days a week.

                G.  ADA/Hazardous Materials.

                      (a)  The Term "Hazardous Substances" as used in this 
Sublease shall include, without limitation, flammables, explosives, 
radioactive materials, asbestos, polychlorinated biphenyl's ("PCB's"), 
chemicals known to cause cancer or reproductive toxicity, pollutants, 
contaminants, hazardous wastes, toxic substances or related materials, 
petroleum and petroleum products, and substances declared to be hazardous or 
toxic under any law or regulation now or hereafter enacted or promulgated by 
any governmental authority.

                      (b)  Sublandlord represents and warrants that to the best
of its knowledge, (I) no Hazardous Substances have been stored, used, spilled,
released, located or disposed of, on or under the Subleased Premises (except a 
full storage tank for the emergency generator serving the building), and (ii)
the Building and the use thereof conform and are not in violation of any
federal, state or local laws, rules or regulations regulating or governing the
use, generation, storage, transportation or disposal of Hazardous Substances
("Laws").

                      (c)  Sublandlord covenants and agrees that it will not 
use or allow the Subleased Premises to be used for the storage (except as 
stated above), treatment or disposal of any Hazardous Substances, and 
Subandlord shall continue to comply with such laws with respect to the 
Subleased Premises.

                      (d)  Sublandlord shall indemnify and hold harmless 
Subtenant, its parent, their respective subsidiaries and affiliates, and the 
agents, officers, directors, shareholders, partners and employees thereof from 
all fines, suits, procedures, claims, losses, and actions of every kind and all
costs associated therewith to the extent resulting from the storage, use,
spillage, release, location or disposal of any Hazardous Substances in, on or 
under Subleased Premises whether or not Sublandlord has acted negligently with 
respect to such Hazardous Substances, excepting any Hazardous Substances in, 
on or under the Subleased Premises resulting from Subtenants's use, handling, 
generation, treatment, storage, disposal or release of any Hazardous Substances
at or from the Subleased Premises.  Sublandlord's obligations and liabilities
under this paragraph 24 (G) shall survive the expiration or sooner termination
of this Sublease.

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             (e)   Sublandlord hereby acknowledges that Subtenant shall arrange 
for a Phase I environmental site assessment to be conducted of the Subleased
Premises (the "Assessment").

             (f)  Sublandlord represents that the Premises shall be in 
compliance with ADA as of the Commencement Date.  In the event Subtenant
performs any alterations to the Premises during the Term which triggers an ADA
modification, Subtenant shall be responsible at Subtenant's sole cost and
expense to comply with ADA requirements.  Except insofar as same is Subtenant's
obligation  pursuant to the preceding sentence, in the event Sublandlord
receives any notices of non-compliance with ADA Sublandlord shall promptly, at
Sublandlord's sole cost and expense comply with ADA requirements.

        H.  Condemnation.

             (a)  If title to any part of the Premises is taken for any public 
or quasi-public use by virtue of the exercise of the power of eminent domain or
by private purchase in lieu thereof, or if title to so much of the Building of
which the Premises are a part is taken that a reasonable amount of
reconstruction thereof will not in Sublandlord's reasonable discretion result
in the Premises or the Building being reasonably suitable for use for the
purpose for which they are designed, then, in either event, this Sublease shall
terminate, on the date that the condemning authority actually takes possession
to the part so condemned or purchased.

             (b)  If this Sublease is terminated under the provisions of this 
Section, rent shall be apportioned and adjusted as of the date of termination. 
Subtenant shall have no claim against Sublandlord or against the condemning
authority for the value of any leasehold estate or for the value of the
unexpired term of this Sublease.

             (c)  If there is a partial taking of the Premises or the Building 
and this Sublease is not thereupon terminated under the provisions of this
Section, then this Sublease shall remain in full force and effect, and
Sublandlord shall, within a reasonable time thereafter, repair and restore the
remaining portion of the Premises, should they be affected, to the extent
necessary to render the same tenantable, and shall repair or reconstruct the
remaining portion of the Building to the extent necessary to make the same a
complete architectural unit.

             (d)  All compensation awarded or paid when a total or partial 
taking of the Premises or the Building shall belong to and be the property of
Sublandlord without any participation by Subtenant.  Nothing herein shall be
construed to preclude Subtenant from prosecuting any claim directly against the
condemning authority for loss of business, moving expenses, and damage to, and
cost of removal of, trade fixtures, furniture and other personal property
belonging to Subtenant.

             (e)  After any partial taking of the Premises which does not 
result in a termination of this Sublease, the Base Rent and Subtenant's
proportional share of Expenses of

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Operation for the remainder of the term hereof shall be reduced by the same
percentage as the floor area of the space taken bears to the total floor area
in the Premises.

                I.  Estoppel.

                      Subtenant does hereby agree that, within twenty (20) days 
following request of Subtenant by Sublandlord by Prime Landlord or by Prime 
Landlord's mortgagee, Subtenant shall deliver to such requesting party, in 
form reasonably satisfactory to such requesting party, a written statement to 
the effect that there are no defaults of Sublandlord or Prime Landlord or 
defenses or offsets against Prime Landlord under this Sublease, that the 
Sublease (plus any modifications and amendments shall be identified) is 
unmodified and in full force and effect, that the rent has commenced to accrue,
that the rent and all other charges have been paid as of the date to which such
charges have been paid and that Subtenant has accepted and is occupying the 
Premises.

                J.  Quiet Enjoyment.

                      Sublandlord covenants and agrees that Subtenant shall 
have complete and quiet enjoyment of, and may peaceably enjoy, the Subleased 
Premises.

                K.  Restoration.

                      Prime Landlord covenants and agrees with Subtenant that 
in the event of any damage or destruction to the Subleased Premises, to the 
extent repair os required under the Prime Lease, Prime Landlord shall promptly 
undertake such repair and shall diligently prosecute the same to completion.

        WITNESS the signature of the parties of the date first written above.

SUBLANDLORD:
AMERICA SERVICE GROUP INC.


/s/ Michael Catalano
------------------------
Signature

Michael Catalano
------------------------
Print name

Executive Vice President
------------------------
Title

      4/23/97
------------------------
Date

                                      13
<PAGE>   13
SUBTENANT
CITIBANK DELAWARE

/s/ Bernard A. Wash, Jr.
--------------------------
Signature


Bernard A. Walsh, Jr.
---------------------------
Print name                      
                                
                                
Vice President
---------------------------
Title

        4-22-97
---------------------------





PRIME LANDLORD:
COMMONS DEVELOPMENT GROUP

/s/ Carmen J. Facciolo Jr.
---------------------------
Signature

Carmen J. Facciolo, Jr.
---------------------------
Print Name

           6P
---------------------------
Title

        4/24/97
---------------------------
Date

                                      14