The FBI has released hundreds of previously sealed documents related to Michael Jackson, most of them about a 1992 investigation of a man who threatened to kill the pop star and then-US President George H.W. Bush.

The records include numerous threatening letters sent by the suspect, who the FBI said had falsely claimed to be the son of then-Gambino crime boss John Gotti and was initially ruled mentally incompetent to go to trial.

The suspect, whose name was concealed in the heavily redacted FBI records, eventually pleaded guilty to a federal charge of mailing a threatening communication and was sentenced to two years in prison, the FBI said.

The files, however, included newspaper clippings about the case that identified the man as Frank Paul Jones, a 34-year-old fan obsessed with Mr Jackson's sister, singer Janet Jackson.

According to news accounts at the time, the New York man had been arrested at the White House for an attempted illegal entry, and was arrested a month later on the grounds of the Jacksons' parents home in Los Angeles.

In one letter, the suspect wrote: "If they do not arrest me or solve my problem, I'm gonna attempt to kill President George Bush." In another, he threatens to "commit mass murder at a Michael Jackson concert, if necessary" and to "personally attempt to kill (Jackson) if he doesn't pay me my money."

The files, made public in response to requests under the federal Freedom of Information Act, also reveal the FBI's role in assisting California police in investigating child sexual abuse allegations against Mr Jackson, who died in June at age 50.

The first case in 1993 was closed without authorities bringing charges against Mr Jackson, who ultimately settled a related civil action for more than $20 million. In 2005 a jury acquitted Mr Jackson of molestation charges in a separate case.