A founder of the now-disbanded Minuteman border patrol group has been convicted in Arizona of molesting a 5-year-old girl, bringing to an end a case that gained the attention of the nation’s highest court after he tried to cross-examine the young victim.

The defendant, Christopher Simcox, 55, was found guilty Wednesday of molesting the girl, who was a friend of his 6-year-old daughter, between April 21, 2012, and May 23, 2013, during visits to his apartment, the Maricopa County attorney, Bill Montgomery, said in a statement. Mr. Simcox was in the process of divorcing his wife at the time.

The girl told her mother of the abuse, and her mother called law enforcement.

“The defendant preyed upon a young child while she was meant to be in his care,” Mr. Montgomery said. “This young girl had the courage to come forward to stop the abuse and by doing so revealed his predatory behavior. With this verdict, we have been able to seek justice for this victim.”

Mr. Simcox was found guilty of two counts of molestation of a child and one count of furnishing obscene materials to a minor, the statement said. He was also accused of sexual conduct with another child, but was found not guilty of that charge, Mr. Montgomery said.