One federal official said investigators have contacted Washington-area escort services, two hotels and a limousine company in recent weeks.
The allegations against defense contractor Brent Wilkes were raised by another defense contractor, Mitchell Wade. Wade has pleaded guilty to charges stemming from the bribery conspiracy involving former Congressman Randy "Duke" Cunningham.
Wade is cooperating with investigators as part of his plea agreement. The sources say he has told the investigators that Wilkes secured prostitutes, limousines and suites at two Washington hotels for Cunningham.
Cunningham is serving a nearly nine-year prison term after pleading guilty last November to taking bribes.
According to a story in Saturday's Washington Post, investigators are also looking at alleged dealings between Christopher D. Baker, president of Shirlington Limousine and Transportation Inc., and Brent R. Wilkes, a San Diego businessman, currently under investigation for bribing Cunningham in return for millions of dollars in federal contracts, said one source.
Cunningham, who collected $2.4 million in homes, yachts, antique furnishings and other bribes on a scale unparalleled in the history of Congress,to eight years and four months in prison, the longest term meted out to a congressman in decades.
Cunningham, who resigned from Congress in disgrace last year, was spared the 10-year maximum by U.S. District Judge Larry Burns but was immediately taken into custody. He also was ordered to pay $1.8 million in restitution for back taxes and forfeit $1.85 million in valuables he received.
Meanwhile, the race to fill Cunningham's seat in Congress is underway.
Earlier this month, Francine Busby, a Democratic school board member easilyand a lobbyist and former Republican Rep. Brian Bilbray appeared to have secured the chance to challenge her.
The second- and third-place finishers were fewer than 900 votes apart in the unofficial tally, though, and Republican Eric Roach considered that too close to call.
The winner of the June 6 runoff will serve the remaining eight months of Cunningham's term.