A Criminal Court jury on Wednesday found Derek Morse guilty of three counts of first-degree murder and attempted murder in a massacre at a Lookout Valley trailer park.
He was sentenced to life in prison without the possibility of parole after a hearing in which witnesses were called.
John "Jake" Lang, Caleb Boozer and Jon Morris were killed and Matthew Callan left for dead at the Rolling Hills Trailer Park on Kelly's Ferry Place on April 9, 2014.
Still facing charges are Skyler Allen and Jacob Allison.
Prosecutors said Allison was driving Morse's car and that Morse and Allen were the gunmen.
Some of the victims were killed as they pleaded for their lives, it was testified.
The attack followed an incident five days earlier in which Morris arranged pay-back to Morse for allegedly taking $20 he was not entitled to in a drug deal.
At the sentencing hearing, the uncle of Morse said the defendant had alcoholic parents. He said the father had disappeared and took no part in raising him. He said his nephew "raised himself" and was without any family structure.
The jury also heard from several members of families of the three victims.