After the Boston Marathon bombings, new forensic evidence linking Tsarnaev to the triple murders was found. Plus, the bomber knew one of the victims and was one of the last people to see the victims alive earlier that day. Although most evidence is circumstantial, it seems like that Tsarnaev had some link to the victims who were brutally murdered.
I think that as it stands there is no evidence that Tamerlan Tsarnaev was involved in the Waltham triple homicide. Some murders will simply go unsolved, unfortunately. I do think that it's a shame Tamerlan died before he could be tried for his crimes at the Boston Marathon, though. But at least we got his brother.