The FBI has reason to believe U.S. Rep. Bob Brady unlawfully concealed a $90,000 payment made by his campaign to get an opponent to quit a 2012 primary race, according to court documents that confirm the Philadelphia Democrat is under investigation in a widening campaign finance probe.

In unsealed court documents made public Monday, the FBI requested a search warrant and has obtained data from an email account belonging to Brady. The FBI agent who filed the warrant wrote that there is probable cause Brady violated contribution limits and produced false documents, and there is evidence that he and others knowingly circumvented campaign finance rules.

Brady has not been charged with a crime. His attorney, James Eisenhower, said that the congressman already has given the emails to authorities and that Brady has done nothing wrong.

"The congressman has not been charged and we have not been informed that he's even a target," Eisenhower said.

The primary opponent and a former aide already have pleaded guilty to concealing the payment. Two political consultants also have been charged in the case.

The warrant, which was executed earlier this month, states that Brady and his primary challenger agreed that the payment "would be disguised" and that the deception would include hiding some of the money under the purchasing of a political poll.

"The evidence shows that these concealed payments were made for the purpose of removing Brady's primary opponent from the race and willfully undermining various provisions of the Federal Election Campaign Act in the process," according to the filing.