Boston police are looking into the possible connection of dead Boston bombing suspect Tamerlan Tsarnaev to a grisly triple homicide that involved one of his friends in 2011.

ABC News:

Tsarnaev, the alleged bombing mastermind who died in a fierce gun battle with police early Friday morning, had been training with one of the 2011 murder victims in an attempt to transition from boxing into a possible career in the brutal sport of mixed-martial arts.

The victims were found in a Waltham, Massachusetts apartment. They had their throat slashed, their heads nearly decapitated. Their mutilated bodies were left covered with marijuana.

It was a gruesome scene - but also perplexing to law enforcement. While drugs appeared to factor into the motive, the murderer left both the marijuana and thousands of dollars in cash behind in the Waltham apartment. While the investigation has been active for more than a year, authorities acknowledged they have had few leads. 

Two law enforcement sources told ABC News that may now change, with the bomb attack prompting a fresh look into Tsarnaev's alleged penchant for violence.

Even before the bombing, police records show, there was an indication of a rage growing inside of Tsarnaev. Court documents obtained by ABC News show in July 2009 he was arrested for domestic violence after his then-girlfriend made a frantic 911 to report she was "being beat up by her boyfriend." The police report, which was redacted to hide the girlfriend's name, says that Tsarnaev admitted to responding officers that he slapped her. The case was later dismissed.

It isn't right to jump to conclusions, but, from the outside, the evidence looks compelling. It may very well have been a drug deal gone bad, but would drug dealers leave behind all that cash and dope?

The speculation for motive in the triple killing is also logical:

One of Mess' relatives yesterday told investigators they thought it was odd that Tsarnaev did not attend the funerals for his slain friend. The Mess relative also described animosity between the two friends "over Brendan's lifestyle,'' two law enforcement sources said. Because it is an open homicide investigation the sources were not authorized to speak on the record.

"Given how religious the older brother was, and we have heard information from the college about how the younger brother was 'a pot head' is there a chance that Tsarnaev was angry that Brendan was selling his brother marijuana? We don't know,'' said one of those sources. "But we are certainly interested in finding out."

We may never know the truth in this case, but it would help fill out the personality and mindset of Tamerlan Tsarnaev if it turned out he committed this bloody crime.