India, July 11 -- The day after conservative youth leader Charlie Kirk was fatally shot in the neck before a crowd of thousands at Utah Valley University, his accused killer paced frantically around a St. George apartment, broke into tears, and confessed to his romantic partner that he deeply regretted the act, according to newly released evidence.

"I just asked him in person if what he said was true the night before, and he said it was," Lance Twiggs, the former roommate and romantic partner of defendant Tyler Robinson, said in a recorded interview with law enforcement played in a Utah County courtroom. "He started crying a little bit and said he wishes he hadn't done it."

The dramatic video disclosure came during the fourth day of a p...