Prior to his execution in 1989, Bundy confessed to killing 30 women across seven states.
Browne said that wasn't even close.
"Ted told me things he'd never told anybody," Browne told KCPQ-TV, Seattle. "He told me he killed more than 100 people, and not only women."
Browne said Bundy's long list of female victims actually began with the murder of a man.
"That's never been known," he said.
Bundy signed a release before his death giving Browne permission to publish information about him but Browne couldn't bring himself to write anything for a number of years.
"I didn't want to visit those dark places again," he said.
Browne said he became more frightened by Bundy after revisiting his relationship with the serial killer.
"Most sociopaths never admit they're evil at all," he said. "Ted really knew he was evil. Evil, evil, evil. And believe me, really evil."