BOSTON -- Amy Bishop, the Alabama professor accused of gunning down three colleagues, and her husband James Anderson were named as suspects by federal investigators in their investigation of a 1993 attempted mail bombing, according to investigative files from the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives.

The documents, released to Team 5 Investigates under a Freedom of Information Act request, repeatedly refer to Bishop and Anderson as suspects in the attempted bombing of Dr. Paul Rosenberg of Newton, Mass., during a two-year period the couple was under investigation.

A witness told investigators that Anderson was angry at Rosenberg and that "he wanted to shoot him, bomb him, stab him or strangle" him after Rosenberg had given Bishop a bad job review for her work at Boston's Children's Hospital, Team 5 Investigates reported.

"That was from an unreliable witness," Anderson said in an interview with Team 5 Investigates Kelley Tuthill.

Rosenberg has said he played a role in Bishop's resignation as a research fellow. A pipe bomb package was sent to his home weeks later.

The documents are heavily redacted and do not name any individual. However, a source close to the investigation identified Bishop and Anderson as the individuals under investigation.

The documents say Bishop was "reportedly upset and on the verge of a nervous breakdown."

During the two years the couple was under investigation, federal agents executed search warrants of the couple's home and informed them of their Miranda rights.

"I suppose it wasn't the only search warrant in this case," said Anderson, who claimed he and his wife were among a number of innocent people questioned by investigators who cast a wide net.

Neither Anderson nor Bishop were charged. The files released do not explain how the investigation concluded.

"There was never any indictment, arrest, nothing, and then everyone was cleared after five years," Anderson said.

Rosenberg and his family fled their house after discovering the bomb and were not injured.

The Harvard-educated Bishop, 45, remains jailed in Huntsville, charged with capital murder and attempted murder in the Alabama shooting, which also wounded three other colleagues.