In the video, you see 19-year-old Cruz being interviewed by an investigator shortly after police apprehended him, and Cruz tells himself he deserves to die because he's "nothing but worthless s**t."

One of the most harrowing parts of the nearly 12 hours of footage shows Cruz sitting by himself and staring into the overheard camera ... pointing his fingers at his head -- like a handgun -- and saying, "Kill me." He also starts sobbing.

Cruz explains to the investigator that he hears voices in his head that tell him to "burn, kill, destroy" -- and he blames the voices for instructing him to pick out the gun used in the Feb. 14 shooting.