The leader of a Michigan militia group charged this week with conspiring to kill law-enforcement officers was described Tuesday as a private, family-oriented man who nurtured a festering mistrust of governmental authority, according to people close to the family.

"On the inside of this man's brain, something evil lurks, and until you get to know him, you don't know it," said Andrea Harsh, who was engaged to David Brian Stone Sr. until the couple broke up last year.

She...