The phone-hacking and bribery scandal roiling Rupert Murdoch's British media empire took a big leap across the ocean Thursday, as the FBI opened an official review of charges that Murdoch's now-defunct News of the World tabloid had tried to steal personal information from the phones of victims of the Sept. 11, 2001, terrorist attack. At least six members of Congress are calling for a close look into the tabloid's U.S.-based parent company, News Corp., and on Friday, Rebekah Brooks, "Murdoch's loyal lieutenant" in Britain, stepped down in the face of a widening scandal. Here, a brief guide to the FBI probe, and the threat to Murdoch's media juggernaut:

What is News Corp. accused of doing?
On July 11, British tabloid The Daily Mirror reported that its rival News of the World had tried (unsuccessfully) to bribe an ex-New York police officer to help hack the phones of 9/11 victims, especially Britons, right after the 2001 attack. The Mirror only quotes one anonymous source to back up its claims. Rep. Peter King (R-N.Y.) and other lawmakers asked the FBI to look into the allegations. 

Is there any other evidence to back up the accusation?
No, according to several law enforcement and congressional officials, including Sen. John McCain (R-Ariz.) — at least none they are aware of. "We don't know what the FBI knows, of course," says Dean Starkman in the Columbia Journalism Review, or what prompted King to call for the investigation. But if the whole case hangs on the one "dodgy" Mirror story, "it's basically bollocks, or whatever they say over there." Well, the FBI is hardly "going off on a lark," says former federal prosecutor Jeffrey H. Cramer, quoted by Bloomberg. "9/11 victims are held dear. If there's even some allegation that they've been victimized again, absolutely they're going to look into it."

Could the U.S. prosecute a defunct British tabloid?
Probably. Ronald S. Safer, another former federal prosecutor, says News Corp. is vulnerable to illegal wiretapping and wire fraud charges. If the feds "find that there was hacking into those accounts that amounts to an unlawful intercept, then they will prosecute," Safer tells Bloomberg. "I do not think that they will defer to U.K. authorities." There are some questions over jurisdiction and statutes of limitations, though, reports The Washington Post. If the FBI does file charges, it would probably be under the Foreign Corrupt Practices Act (FCPA), which criminalizes foreign bribery by U.S.-based companies.

Should Murdoch and Co. be worried?
It would be very hard for the FBI to prove that News Corp. journalists had tried to hack 9/11 victims' phones, "unless they have someone on the inside of the scheme who is providing information," says legal expert Roland Riopelle, quoted by Reuters. The close ties between News Corp. and its U.K. subsidiary, though, may make "Murdoch and his companies vulnerable to U.S. prosecutions even if the scandals are limited to Britain," says Peter Goodspeed in Canada's National Post. And even if federal investigations go nowhere, the legal bills will probably cost Murdoch millions.

Sources: APBloomberg, CBSCNETColumbia Journalism Review, Daily MirrorNational PostReutersWashington Post