Initial testing of evidence found at the scene may also link his brother Dzhokhar Tsarnaev to the murders, the source said. Additional testing is under way, according to the source, who said the brothers made cellphone calls from an area near the crime scene around the time of the murders.
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Newsday has reported that Tamerlan Tsarnaev was a friend and fellow boxer of one of the victims, Brendan Mess, with whom he trained.
Mess, Erik Weissman and Raphael Teken were found dead, their throats slit, in Waltham, Mass., on Sept. 12, 2011.
Tamerlan Tsarnaev was killed in a shootout with police four days after the marathon bombings; his brother was later found hiding in a boat in a suburban backyard and is being held on federal terror charges. Three were killed and more than 260 injured when two bombs exploded near the finish line of the Boston Marathon.
The source says local authorities are probing whether religion played a role in the grisly murders, since Weissman and Teken had Jewish roots.
The source also said the murders may have taken place on Sept. 11 and local investigators are looking into whether the anniversary of the terrorist attacks played any role.
Meanwhile, Tamerlan Tsarnaev has been buried in a Muslim cemetery in Virginia, according to his death certificate.
He was buried at Al-Barzakh Cemetery in Doswell, according to the certificate. Doswell is a small town about 22 miles from Richmond.
In a news release Thursday, Worcester police said a "courageous and compassionate" person came forward to "provide the assistance needed to properly bury the deceased. His body is no longer in the City of Worcester and is now entombed."
A source identified that individual as a Virginia resident who coordinated with the Islamic Society of Greater Richmond to bring the body to that state. The society did not immediately return a call seeking comment yesterday. The cemetery could not be reached.
The body was previously in the custody of Tsarnaev's uncle, Ruslan Tsarni. Tsarnaev's widow, Katherine Russell, asked to have his body released to her in-laws. Tsarni is named on the Massachusetts death certificate as having handled the removal of his nephew's body from the state.
After the April 19 shootout with police, Tsarnaev, 26, was pronounced dead at Beth Israel Deaconess Medical Center in Boston of "gunshot wounds of torso and extremities" along with "blunt trauma to head and torso," the certificate said.
Tamerlan Tsarnaev had been "shot by police and then run over and dragged by motor vehicle," driven by his brother Dzhokhar Tsarnaev, 19, in Watertown, Mass., the certificate said.