Former associates of slain Boston Marathon bombing suspect Tamarlan Tsarnaev now believe he may have been involved in a 2011 triple murder that claimed the life of his closest American friend, Brendan Mess.

"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. Tam's name wasn't coming up at all," said one of their mutual friends, who asked to be identified by his first name, Ray.

Now "a few of my friends, without even speaking about it beforehand, have all been thinking" that Tsarnaev could have been connected to the 2011 murder of Mess and two others at Mess' apartment, he said. Ray and Tsarnaev were both part of a social circle centered on the gym at which Tsarnaev trained and on a Boston hip-hop group called FlyRidaz, whose members this week expressed shock at having known the suspected killer.

Ray gave BuzzFeed his full name but asked that it not be used because, he said, he is concerned for his safety. Other friends were more reticent about speaking with reporters. But some have been reflecting on their knowledge of Tsarnaev on social media.

"This is so crazy. Lots of us knew the older suspect. UNREAL AND TERRIBLE," a former friend wrote.

"I just put together what this meant and I'm buggin the fuck out," responded another.

The 2011 murder has returned abruptly to the forefront of their minds.

The owner of the Wai Kru Mixed Martial Arts in Allston, John Allan, told reporters that Tsarnaev described Mess to him as his "best friend."

So the Cambridge crew were surprised in the fall of 2011 that Tsarnaev didn't show up at his best friend's funeral. Now they see it as 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 when he said, 'I don't have any American friends.'"

"He was somebody who was in contact with Brendan on a daily basis. Anybody like that, you would think they would have been around," Ray said.

The other members of their social circle recalled Tsarnaev, 26 at the time of his death Thursday, as a "normal guy" who liked boxing and occasionally came to their rap shows.

He "wore regular American-ish clothes," said Ray, also 26, who said he lost touch with him directly after the murder of Mess, along with Raphael Teken, 37, and Erik Weissman, 31 on Sept. 12, 2011, in nearby Waltham.

Ray said he had met Tsarnaev in 2010. He and his friends had an amiable, if not particularly close, relationship with him, and didn't think of him as different. They didn't notice any increasing religious fervor, which Tsarnaev is said to have developed in the last two years.

"He kind of had an accent, but I didn't think of him as that foreign," he said. "He was sociable but kind of distant."

Tsarnaev met the rappers through Mess, Tsarnaev's gym buddy who lived down the block from him. Tsarnaev was an aspiring Olympic boxer, and Mess was training in mixed martial arts. "Tam did a lot of training with him in the gym," Ray said. "Brendan was my link to Tam."

Tsarnaev went to Ray's house before a FlyRidaz show once and attended one of their shows, he said.

But contact stopped after the horrific triple murder.

"Those three guys all had their throats cut, and they had marijuana dumped all over their bodies," Ray said. "It's really gruesome how they were killed. It's not something typical you'd see in Waltham. Not some home invasion gone wrong or something."

Police indicated the three men had "sharp force injuries of the neck" and $5,000 was left at the scene, and they believe the murders were "targeted and not a random act of violence."

Police have said they believe there were two other men in Mess' apartment — the scene of the crime — sometime before the murder, but those two men have never been identified. Ray said following the murder, he was questioned by detectives who told him Tsarnaev may have been with Mess either the day of or the night before, although the Middlesex County District Attorney's Office said they could not confirm any relationship between Mess and Tsarnaev. The Waltham police department declined to comment on the murder or on the alleged relationship between Tsarnaev and Mess.

After Tsarnaev was fingered as a suspect in the Boston Marathon bombings, Ray and his friends became increasingly convinced he had something to do with the gruesome 2011 crime.

They originally suspected Mess' girlfriend, an immigrant from Somalia, they thought, whom Ray described as a "transient" who "latched onto Brendan." She had a friendly relationship with Tsarnaev, with whom she would have "conversations about religious things and lifestyles."

The attitude about Tsarnaev's involvement has changed in the last week. Now people suspect him of the worst.

"A few of my friends, without even speaking about it beforehand, have all been thinking this," he said.

"There was no forced entry," Ray said, so police believe whoever was responsible was let into the apartment.

No suspects have ever been named, but Waltham police said the case is still open.

A few months after Mess' murder, Tsarnaev went to Russia for six months. His father, Anzor Tsarnaev, told the Associated Press his son stayed with him in the city of Makhachkala, in the region of Dagestan.

"He slept until 3 p.m., and you know, I would ask him: 'Have you come here to sleep?'" his father said. "He used to go visiting, here and there. He would go to eat somewhere. Then he would come back and go to bed."

When Tsarnaev returned to the United States, Ray said a friend saw him out in public once and described him as "hollow." But Mess' younger brother continued to see Tsarnaev at the gym where they both trained. "Tam was with Brendan's little brother a month ago," he said.

Ray said none of his friends saw any "red flags" while they were friends with Tsarnaev, although he said some of them remember Tsarnaev making comments about the afterlife being glorified and disparaging remarks about Americans once or twice.