Tamerlan Tsarnaev may have also murdered his “only American friend” Brendan Mess in an unsolved triple killing in 2011, it emerged today.

Brendan Mess was found with his “throat slit” alongside two other men in a Massachusetts apartment in 2011 in what police described as a “very graphic crime scene”.

Former associates of Boston bomber Tamerlan Tsarnaev didn’t initially suspect him of carrying out the gruesome attack, but thought it was strange he didn’t attend his friend’s funeral.

Now one man who knew Tamerlan Tsarnaev through the gym where they trained said some of their social circle “without even speaking about it beforehand have all been thinking” he could be involved.

One friend, who gave his name only as Ray, told BuzzFeed Politics: “At the time, none of us would have thought it was Tam.

“It was just so emotional and we thought we had someone else who had done it.”

Brendan Mess was found with his “throat slit” alongside two other men in a Massachusetts apartment in 2011

But since Tamerlan Tsarnaev was identified as the suspect in the Boston Marathon bombings that killed three and injured 180, Ray believes his sudden disappearance after Brendan Mess’s death may be a clue.

“Tam wasn’t there at the memorial service, he wasn’t at the funeral, he wasn’t around at all,” Ray said.

“And he was really close with Brendan. That’s why it’s so weird.”

Ray said he met Tamerlan Tsarnaev in 2010 when they were part of a social circle that centered on the Wai Kru Mixed Martial Arts gym in Allston, Massachusetts, where Tsarnaev trained as a boxer and had a shared interest in the Boston hip-hop group FlyRidaz.

He said they had a friendly, but not particularly close relationship and described Tamerlan Tsarnaev as a “normal guy who wore regular American-ish clothes”.

Their contact stopped when Brendan Mess and two other men – Raphael Teken and Erik Weissman – were murdered on September 12, 2011.

Their bodies were found covered in marijuana in an apartment in Waltham, Massachusetts, and had their throats slit with a knife or ice pick and around $5,000 was left at the scene.

Brendan Mess’s girlfriend discovered the bodies, she ran from the house screaming.

Initially police said two other people had been there on the day and they were looking to question them, although no one has ever been charged.

Ray said there had been no forced entry, so police believe the killer was known the victim and was let into the apartment.

Investigators at the time said the murders were “targeted and not a random act of violence”.

Middlesex District Attorney Gerard Leone issued a statement soon after the murders saying: “Based on the present state of the investigation, it is believed that the victims knew the assailant or assailants, and the attacks were not random.”

Neighbors described Brendan Mess and his two roommates as quiet, nice people who were a welcome change of pace from previous residents who often had loud parties late into the evening.

Indeed, at the time of the killing, police and Brendan Mess’ friends suspected his girlfriend, an immigrant from Somalia that Ray describes as a “transient” who “latched onto Brendan”.

Ray described her as having a good relationship with Tamerlan Tsarnaev and that they would have “conversations about religious things and lifestyles”.

In 2008, Erik Weissman was charged with marijuana possession and intent to distribute, according to a report.

Police pulled Erik Weissman over for failing to yield and smelled marijuana smoke in the vehicle.

When asked about it, Erik Weissman said: “I knew you would smell it,” and handed the officer a brown paper bag filled with bags of marijuana, police said.

A year earlier, Tamerlan Tsarnaev claimed to have just one American friend despite spending much of his life in the US.

Indeed, Tamerlan Tsarnaev introduced Brendan Mess as his best friend to the owner of the gym.

Wai Kru Mixed Martial Arts center owner John Allan said Tamerlan Tsarnaev and Brendan Mess used to work out at his gym together but Tsarnaev stopped coming after Mess was murdered.

The event clearly still haunted Tamerlan Tsarnaev as recently as last week when he suddenly returned to his old gym and started acting unusually.

The business owner who was traveling in Thailand at the time said he received an e-mail saying Tamerlan Tsarnaev had been in, but acted rudely and disrespectfully to other gym-users.

“It was a clear indication that something was up,” John Allan told the Boston Globe.

“He was becoming a complete [expletive].”

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