The FBI has begun several internal investigations, including at least one that could result in criminal charges, over leaks to the media about public corruption probes shortly before last month's elections.

At least one of the alleged leaks involves the federal inquiry of Rep. Curt Weldon, R-Pa. He lost his House seat weeks after the FBI raided the homes and offices of his daughter and her business partner.

"There are a series of investigations we've undertaken, some by our inspection side, and some, at least one we're looking at as a criminal investigation," FBI Director Robert Mueller told the Senate Judiciary Committee on Wednesday.

"Although I usually say I can neither confirm nor deny an investigation, I think it's fair to say in this particular case we are pursuing it, and by that I mean (the leak involving) Congressman Weldon," Mueller said.

Mueller described himself as "exceptionally disappointed, and that is being charitable, in terms of my response upon hearing about the leak."

On Oct. 13, McClatchy Newspapers reported that the FBI was looking into whether Weldon illegally steered $1 million in contracts to his daughter's lobbying firm. Agents followed up with the raid three days later, in part out of fear that evidence would be destroyed after the investigation was exposed.

Officials also confirmed federal investigations of several other House lawmakers that month, including former Rep. Mark Foley, R-Fla., and retiring Rep. Jim Kolbe, R-Ariz. All three men have maintained their innocence.

Senators scolded Mueller about the leaks. The committee chairman, Sen. Arlen Specter, R-Pa., said the disclosures were "just disastrous" for suspects who have not been charged, much less proven guilty.

Similarly, Sen. Charles Grassley, R-Iowa, lectured Mueller about refusing to brief lawmakers about the FBI's continuing investigation of the 2001 anthrax attacks — even though many sensitive details were reported in several newspapers.

"This looks like an example of the FBI's left hand not knowing what the right hand is doing," Grassley said. "You're telling me that you won't answer questions about the anthrax investigation, while someone else is telling the public that you're keeping us fully informed."

Leak investigations at the FBI, particularly those that could bring criminal penalties, are rare, former agents and experts said. They are hard to prove, particularly if some of the information has already been reported in the media or revealed in court documents.

Disclosing information a grand jury is considering is a serious crime, and such leaks often aim "to sway public opinion in favor of the government," said Martin Pinales, president of the National Association of Criminal Defense Lawyers.

"They also have the possibility of swaying the jury pool down the road," Pinales said. "So, in that context, they're a problem."

On the other hand, leaks may sometimes be the price of having an open government in a democracy, said Ronald Collins, a scholar at the First Amendment Center.

"Legally, those who leak do so at their own peril," Collins said. "Does the public's right to know, does knowledge of our government depend on leaks — including illegal leaks? Unquestionably."

FBI agents can be forced to take lie-detector tests or otherwise cooperate with investigations to avoid losing their security clearances, and in turn, their pay. Information about ongoing criminal cases generally is shared with prosecutors and other law enforcement authorities — widening the scope of suspects in leak cases.

Fred Bragg of the FBI Agents Association said his group "would invite a strong look at any leak matter — and we look forward to those results."