29-year-old John Lee Cowell took the witness stand in his own defense as scheduled on Tuesday, after the prosecution rested its case on Monday. And he unleashed some choice quotes that may bolster an insanity defense.

Because the prosecution does not have to prove whether Cowell killed 18-year-old Nia Wilson in July 2018, or whether he also stabbed her sister Letifah in the neck — his defense attorney made clear that he did it in opening statements last week — their case was made quickly. It included multiple viewings of surveillance video at the MacArthur BART station showing the moments before, during, and after the knife attack that took Wilson's life and injured her sister.

Letifah and sister Tayisha Wilson, who was also present at the station that day, both gave tearful testimony on Monday, as CBS SF reports. Tayisha said she saw her sister Nia stumble and cry out for Letifah after being stabbed. And BART police Officer Andres Rocha testified about trying to save Nia's life and "keep her heart beating" as he performed CPR.

Cowell, who was briefly removed from the courtroom during the prosecution's opening statements last week, has been absent from the trial for the past two days without explanation, according to ABC 7. Defense attorney Christina Moore is seeking to establish Cowell's mental state at the time of the murder. She has said that he was diagnosed schizophrenic six years before the killing occurred, and that he is "genuinely, severely and tragically impaired." Moore attempted multiple times to have Cowell declared unfit to stand trial, but psychiatric experts disagreed, and after over a year in jail decided he could stand trial.

Moore has said that Cowell was hearing voices when he stabbed the Wilson sisters.

Update: After taking the stand, Cowell made a "series of bizarre ramblings," per KPIX, saying that he hears "voices in his head that came from alien technology implanted in his ear with aliens using a radio to communicate with him." He went on to say that the Wilson sisters were aliens in "skin suits" who were threatening to kill him, and that he needed to attack them in order to save them from hurting his grandmother, which he says they were threatening to do. He also said the women were "standing over him" and threatening him prior to the stabbings, which is contradicted by surveillance video from the scene.

Previously: Nia Wilson Murder Trial Begins With Gruesome Surveillance Video, Outburst From Accused Killer