WASHINGTON - Allentown Mayor Ed Pawlowski suspended his campaign for the Senate on Monday, four days after FBI agents executed search warrants at Allentown City Hall.

In a statement, Pawlowski said he was pausing the campaign "to fully focus on assisting in the federal investigation of Allentown contracting practices both prior to his being elected and since." He said he would reevaluate when he had a clearer picture of the investigation.

The news came after agents raided the office Thursday, seized documents, and interviewed Pawlowski and city Managing Director Francis Dougherty, according to a source close to the investigation.

It was not clear if Pawlowski and Dougherty are targets in the investigation or potential witnesses. An FBI spokesman declined to comment.

A woman who answered a phone number listed for Lisa Pawlowski - the mayor's wife and campaign treasurer - would not say Monday afternoon if the campaign was still operating.

"We're cooperating fully with an investigation right now, so we've been asked not to say anything about that," she said. She declined to identify herself and ended the call.

Ed Pawlowski was seen as a longshot candidate, but was one of only two Democrats in the field, along with Joe Sestak, the former congressman from Delaware County.

Some Democrats in Washington and Pennsylvania have been seeking alternatives to Sestak, who is seen by some party officials as too much of a maverick to take on the Republican incumbent, Sen. Pat Toomey, in what is being billed as one of the country's top Senate races.

The latest big name in the mix is Katie McGinty, Gov. Wolf's chief of staff.

Several Democrats said McGinty had spoken with national party leaders about the race. But how serious those conversations are - and how interested McGinty and the national party are - was unclear Monday.

Democratic insiders questioned whether McGinty, a Philadelphian who lost the Democratic primary for governor last year, would leave Wolf's administration just months into his tenure.

The national party had tried to recruit Montgomery County Commissioner Josh Shapiro, who declined to run for Senate, and has talked to other potential candidates.

"There are still folks that are looking at the office in a serious fashion and considering whether or not they should throw their hat into the ring," said Jim Burn, chairman of the Pennsylvania Democratic Party.

Sestak has a big money lead, but "you will see, between now and next May's primary, more than one trial balloon for more than one name for U.S. Senate, I can assure you," Burn said.

Pawlowski, mayor of Pennsylvania's third-largest city, might have seen his hopes dashed by the FBI raid on Thursday.

Since then, his top political hand, Mike Fleck, has been out of the public eye. His cellphone number has been disconnected, and he did not respond to e-mails.

Daryl Nerl, a former employee at Fleck's firm, H Street Strategies, said he received an e-mail from a lawyer Monday informing him that his "employment was terminated" as of Thursday, "due to the dissolution" of the firm.

The e-mail came from Brian Monahan, a Lehigh Valley defense attorney whose work ranges from traffic tickets to felonies. Monahan did not respond to a call and e-mail seeking comment Monday.

Pawlowski had done little public campaigning since launching his run in April, saying he intended to focus on fund-raising. His website included little besides an introductory video.