BOSTON (REUTERS) - An autopsy on Boston Marathon bombing suspect Tamerlan Tsarnaev determined precisely how he died after a bloody shootout with police but the results can't be made public until the body is claimed, a spokesman for the Massachusetts Medical Examiner said on Monday.

FBI agents also spent hours at Tsarnaev's widow's family home in North Kingstown, Rhode Island, and came out carrying bags market DNA samples, a person familiar with the investigation said

Two law enforcement officials said both the FBI and local law enforcement agencies are now looking beyond the Boston area to try to identify associates or possible confederates of Tsarnaev and his younger brother, Dzhokhar.

A federal official said that further searches by the FBI or other agencies for physical evidence were also possible.

Authorities and the public have been waiting to learn whether Tamerlan Tsarnaev died in a hail of police bullets or when he was run over by Dzhokhar when the younger Tsarnaev fled in an SUV they had stolen.

"The Medical Examiner has determined the cause of death," said Terrel Harris, spokesman for the Massachusetts Office of the Chief Medical Examiner, but added that these findings will not be made public until the body is claimed and a death certificate is filed.

Tsarnaev's widow, Ms Katherine Russell, would be permitted to claim the body from the medical examiner but she has been in hiding at her family's home.

She was seen leaving the house on Monday afternoon with her lawyers and was later seen leaving her lawyer's offices in Providence, Rhode Island.

Police said the Tsarnaevs set off twin bombs on April 15 that ripped through the crowd near the marathon's finish line, killing three and injuring 264.

The Tsarnaevs led police in a wild car chase through metropolitan Boston three days later, throwing grenades and exchanged gunfire as the officers closed in.

Tamerlan Tsarnaev had stepped outside the SUV to shoot at police when he was hit by gunfire and was run over by his brother when the younger Tsarnaev escaped. He was pronounced dead at Beth Israel Deaconess Medical Center.

Dzhokhar, 19, was captured on April 19 and has been recovering from bullet wounds at a prison medical center outside Boston.

Ms Russell said through her lawyer last week that she was doing everything she could do assist officials with the investigation.

Her lawyers have not said anything else, but a person familiar with the matter said they have been negotiating how much access officials will have to their client.

Ms Russell, 24, lived with Tamerlan Tsarnaev and their young daughter in Cambridge, Massachusetts. Police have said they found bomb material in that apartment.

Her lawyers have said she didn't know much because she spent most of her time working as a health aide near Boston while her husband was at home watching the child.

The brothers' parents, now living in Russia, said on Sunday that they have abandoned initial plans to come to the United States to claim their older son's body and visit their younger son.