This page of the Disco Elysium guide contains a detailed walkthrough of the Speak to the Assault Victim quest.
In the Speak to the Assault Victim quest in Disco Elysium, you have to talk to Klaasje - a woman who has allegedly been sexually assaulted by a mercenary nicknamed Lely.
Klaasje will admit that she hasn't been really assaulted by the deceased mercenary. When you ask why the man died, she will answer that he had something to do with the strike - he worked for Wild Pines and against the Union.
It's time to go back to Titus and tell him that Klaasje has confessed you the truth. Titus will not be happy about this and will hand you a recording where the “Soldier of Apocalypse” mercenary allegedly pleads guilty - it will start the Doorgunner Megamix quest.