Italian Ambassador to the DRC Luca Attanasio was among three people killed on February 22, 2021, when a United Nations convoy was ambushed in the DRC's troubled east.
The other fatalities were driver Mustapha Milambo and Italian police officer Vittorio Iacovacci.
During previous hearings, the prosecution cast the defendants as criminals who had initially intended to kidnap the ambassador and demand a $1 million ransom.
The defendants, who were arrested in January 2022, denied any wrongdoing and said their initial confessions were extracted through torture.
Public prosecutors had originally sought the death penalty for the six accused.
Much of eastern DRC is prey to armed groups, many of which are a legacy of regional wars that flared during the late 1990s and early 2000s.
Militia attacks against civilians in the volatile region are common.
