Complex sentence: Brian Kennedy, the owner of Everest Windows, stepped forward in September 2007 to underwrite the search and pay for the salary of Clarence Mitchell, who became the McCanns' spokesperson.
Split into simpler sentences: Brian Kennedy, the owner of Everest Windows, also stepped forward, in September 2007, to help the McCanns financially. As well as helping to finance the search, he paid for the salary of Clarence Mitchell, who became the McCanns' spokesperson.