Blood taken from the floorboards of a Detroit-area house doesn't match Jimmy Hoffa's, the FBI said Monday.

The Detroit Free Press had quoted Bloomfield Township Police Chief Jeffrey Werner as saying the FBI told his detectives that technicians found blood at the house when they went in to investigate last May. He said the FBI didn't think the blood belonged to Hoffa.

The FBI had been alerted to the house because of a FOX News investigation into the mystery surrounding the disappearance of the one-time Teamsters president in 1975.

Frank Sheeran (search) — nicknamed "the Irishman' — was one of the handful of FBI suspects in Hoffa's murder. Sheeran was a local Teamsters president from Delaware who was close to Hoffa. At the same time, he was the right-hand man to a power of a different sort: legendary mob boss Russell Bufalino.

Sheeran, who died last year, told FOX News he was Hoffa's killer, but he refused to make the confession on camera.

"Frank Sheeran actually pulled the trigger," said Charles Brandt (search), one of Sheeran's lawyers. Brandt has written a new book called "I Heard You Paint Houses" (search), which lays out Sheeran's story and is set to be released in June.

The Mystery

Hoffa became the Teamsters (search) leader in 1957 and was sent to prison 10 years later for jury tampering and fraud. He was pardoned in 1971 after giving up the union presidency.

On July 30, 1975, Hoffa disappeared.

That day, he thought he was meeting two mobsters: Anthony "Tony Pro" Provenzano from Union City, N.J., and Tony Giacalone from Detroit. The three were supposed to talk about money and Hoffa taking back the national Teamsters' presidency, a move the Mafia didn't want. Hoffa also expected Sheeran, whom he considered a loyal friend, to be at his side for the sit-down and serve as his backup.

"Jimmy Hoffa had every reason to believe that Frank Sheeran, probably the toughest guy that anybody ever knew, was there to protect him in case of a problem and so Jimmy Hoffa got in the back seat of the car," Brandt told Fox News.

According to Sheeran's story, Hoffa thought they were going to meet at 2 p.m. at the Macus Red Fox restaurant. By 2:15 p.m. Sheeran hadn't shown up, so Hoffa walked across the parking lot and called his wife from a pay phone to ask if his friend had called. He hadn't.

Finally, at 2:40 p.m., Sheeran pulled up, and Hoffa took his last ride.

"What we do know, he would have never gotten in any vehicle unless there was a trusted adviser there," said David Corcyca, the Oakland County, Mich., prosecutor who is handling the case.

Sheeran said they drove 8 miles with Hoffa's so-called foster son Chuckie O'Brien behind the wheel and mobster Sal "Sally Bugs" Briguglio next to Hoffa in the back seat. Their destination: the three-story house in Detroit.

Hoffa and Sheeran got out of the car while O'Brien and Briguglio backed the car up out of the driveway. The union leader and his friend walked up the front steps into the house.

According to Sheeran, once inside a small vestibule, Hoffa realized something was wrong, and he doubled back to get out the front door.

He never made it. Sheeran said he shot Hoffa two times behind the right ear, a mob hit ordered to keep Hoffa from power.

"He's the logical guy to use when you want to whack a guy like Jimmy Hoffa. He's a close friend. He's a guy who Jimmy Hoffa trusted," said Jerry Capeci, an organized crime expert.

Capeci said Hoffa had to go "because he was doing things that were going to upset the apple cart and annoy the Mafia bosses."

Sheeran has told different conflicting stories about what happened to Hoffa.

In 1975, Sheeran invoked his Fifth Amendment rights before a Detroit grand jury investigating the Hoffa disappearance. He once blamed the Nixon administration, said he had a letter from Hoffa that later turned out to be a forgery and even tried to use a legal maneuver to avoid going back to jail.

But near the end of his life, Sheeran finally confessed. And the Hoffa family thinks Sheeran was in on it.

Sheeran's story was that after the murder, he dropped the gun on the floor and left the house. He was told Hoffa's body was cremated.

On Dec. 14, 2003, Sheeran died. He was 83. Just a few weeks before his death, he confirmed his story from his hospital bed. "I stand by what's written in the book," Sheeran said.

FOX News' Eric Shawn and Kendall Hagan contributed to this report.