It was obviously important for Voight to tie up any and all loose ends, even if that witness-surrounded shooting might come back to bite him, and his name was eventually cleared for Bingham’s murder.
(Though he had to get Denny eyed for witness tampering to do so, after already getting too talky with him.)
Beyond his own self-preservation, though, Voight definitely owed Olinsky for knowingly taking the fall there.
The investigation into Olinsky’s stabbing revealed it to be about revenge — go figure — and Voight ended up killing the person who called for the prison hit.