April 29, 2013 -- The stalled investigation into a gruesome 2011 triple murder in the leafy suburb of Waltham, Mass., has taken a dramatic turn in the days since two explosions ripped through the crowd during the final stretch of the Boston Marathon.

In the two weeks since those blasts erupted 12 seconds apart, FBI agents have begun working with prosecutors to interview family members and friends of the three victims in the unsolved Waltham slayings, law enforcement authorities tell ABC News. Family members of two victims told ABC News they had been contacted by FBI agents about the case in recent days. The agents' interest has been sparked by an overlooked connection between accused bomber Tamerlan Tsarnaev and one of the victims in the case, Brendan Mess.

Mess and his two friends; Raphael Teken, 37, and Erik Weissman, 31, had their throats slit late on Sept. 11, 2011, the 10-year anniversary of the 9-11 attacks. Last week, prosecutors confirmed to ABC News that they were trying to determine whether Tsarnaev had any link to the case.

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Both Tsarnaev, 26, a Golden Gloves champion, and Mess, 25, a Jiu-Jitsu fighter, had harbored dreams of a career in mixed-martial arts, a sport which combines skills from both. The two started training together in 2009, and at one point lived as roommates, relatives told investigators. In the months before the slayings, friends of Mess said he had been bringing the quiet immigrant along with him to social events.

Scott Wood, 40, an army ranger and instructor at Vermont Brazilian Jiu-Jitsu, befriended and trained Mess when he was briefly a student at the University of Vermont. He says the last time he saw Mess was at a fight event in June 2011. Mess brought Tsarnaev as his guest.

"I met that guy at a fight event. Brendan introduced me to him as Tam,'' Wood told ABC News. "He seemed like a real arrogant guy, the tough guy at the gym, not a mass murderer."

Another friend of Mess's told ABC News he, too, remembered Tsarnaev joining the group to watch a mixed-martial arts fight. The friend, who spoke on the condition he not be identified, said Mess and his friends kept calling Tsarnaev "champ," because of his Golden Gloves title. Tsarnaev was quiet, he said, sitting at the end of the row and declining when people offered him beers.

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Last week, another strange link emerged between the accused Boston bomber and the triple murder case. Investigators were called to the parking lot of Gerry's Italian Kitchen on Belmont Street in Watertown. A Planet Aid driver had stumbled upon discarded fireworks in a donation bin there. Law enforcement sources told ABC News that the gunpowder had been emptied from the fireworks and the shells discarded in a shopping bag inside the bin. Investigators put the bins on a flatbed truck and drove them away as possible evidence in the bombing case.

Gerry's Italian Kitchen also surfaced in the triple murder case.

The last time anyone is known to have heard from the three men was at 8:54 p.m. on Sept. 11, when someone called Gerry's on Weissman's cell phone and ordered meatballs, a chicken cutlet and a side order of sausage. When a delivery woman arrived twenty minutes later there was no answer and no one picked up when they tried to call Weissman's cell phone.

The following day the three men were found with their throats slashed, their bodies mutilated and covered with marijuana. Police were perplexed because the drugs and $5,000 were not taken from the blood-soaked scene and there was no sign of forced entry. At the time the bodies were discovered, local prosecutors said "it does look like the assailants and the decedents did know each other. We have no evidence of a break in the apartment."

A source close to the investigation told ABC News they are trying to determine whether Tsarnaev once worked as a pizza delivery driver at Gerry's Italian Kitchen. The manager and employees of the eatery said in repeated interviews that he had never worked there.

In the aftermath of the Boston bombings, Mess' friends and relatives say they can't let go of suspicions about Tsarnaev.

"It's no coincidence that the last time I saw my friend Brendan alive he was walking out of that fight with that kid Tam,'' Wood said.

Officials in neighboring Somerville told ABC News they are glad prosecutors have started to look more closely at a possible connection.

"After seeing what occurred on Marathon Monday…nothing surprises me anymore,'' Somerville Mayor Joseph Curatone told ABC News. "I hope and I know that law enforcement professionals will dig and we will find out the whole story."

Somerville Police Chief Tom Pasquarello said that the savagery Tsarnaev has been accused of displaying – including the alleged assassination of MIT Police Officer Sean Collier – would indicate that investigators should look more closely at the relationship between the murder victims and the suspected bomber.

"Anyone who would go up to a police officer and has no problem with the cold blooded killing of a police officer would have no problem with that type of murder whether it was over a drug deal or another type of crime,'' Pasquarello told ABC News.

Freelance writer Michele McPhee is a Boston-based reporter and frequent contributor to ABC News.