I think the majority of Salemme's testimony was against Flemmi during his trial as he had recently discovered that Flemmi and Bulger were rats and were responsible for ratting him out more than once and causing a lot of his jail time. A lot was about the 60's gang wars too where most of the people involved weren't around anymore except Flemmi and Bulger.

Although I think he did get into more trouble for not being truthful about a murder, maybe the Steven DiSarro hit that his son may have carried out.