Defendant John Lee Cowell initially refused to enter the courtroom Thursday then was kicked out 15 minutes into his appearance in the Nia Wilson murder trial, prosecutors said.
The trial was delayed Thursday morning as Cowell's attorney tried to convince the 29-year-old transient to enter the Oakland courtroom, where he is on trial in the fatal stabbing of 18-year-old Wilson.
After he relented and came down to continue his testimony, Cowell was removed for using profanity and refusing to answer questions.
Prosecutors said if Cowell failed to complete his testimony Thursday, his previous testimony would be thrown out.
Cowell took the stand Tuesday and said he believed Wilson and her sister were aliens and part of a gang that had kidnapped his grandmother.
"I stabbed both of the females in the crew, because I believed they would not give my grandmother back,'' Cowell said from the witness stand in Alameda County court, the San Francisco Chronicle reported.
Cowell has pleaded not guilty by reason of insanity in Wilson's slaying and the stabbing of her sister, Letifah Wilson, who was seriously injured.
During his testimony Tuesday, he said he has a history of mental illness and heard voices in his head. But he could not remember what those voices told him.
Just before the fatal stabbing on July 22, 2018, Cowell rode the train from Concord to the MacArthur station in Oakland along with Nia Wilson and two of her sisters.
During direct examination, Cowell spoke about a radio in his head and said the three women were "pointing to other passengers while staring at me.''
He added that he felt "threatened by three black females. They were together ... threatening to assault my grandmother."
Surveillance footage of the entire 25-minute ride shows no interaction between Cowell or any of the sisters.
Police said Cowell pulled a hood over his head and put on sunglasses just before the attack. He also allegedly discarded his backpack and clothing in the station's parking lot to avoid arrest. He was taken into custody a day later at BART's Pleasant Hill Station.
Cowell is charged with one count of murder and one count of attempted murder for the double stabbing.