PORTLAND, Ore. --The father of a 7-year-old Portland boy missing for more than a month told a judge he believes the boy's stepmother is involved in the disappearance, according to a court document released Thursday.

The father, Kaine Horman, also said in the request for a restraining order against Terri Moulton Horman that investigators told him that he had been the target of a murder plot by his wife.

The court documents confirmed a report in The Oregonian newspaper on Sunday about the allegation of a murder-for-hire. That report said Terri Horman tried in late 2009 to hire a landscaper to kill her husband.

A lawyer for Terri Horman did not immediately return a call Thursday.

Kyron Horman, a second-grader, disappeared June 4. Investigators say Terri Horman was the last person to see him. She reported she left him at his school after an early-morning science fair.

Investigators have not named her as a suspect or a person of interest, but in recent weeks they have focused their investigation on her.

Kaine Horman has filed for divorce, and a judge granted the restraining order against Terri Horman. The petition for the order was unsealed Thursday.

"I believe respondent is involved in the disappearance of my son Kyron who has been missing since June 4, 2010," Kaine Horman's petition reads. "I also recently learned that respondent attempted to hire someone to murder me. The police have provided me with probable cause to believe the above two statements to be true."

An attorney for Kaine Horman did not immediately return a phone call.

The couple was married in April 2007 and have a 19-month-old daughter. She also has a teenage son from a previous marriage.

According to court documents, Kaine Horman moved out of the family home shortly before filing the divorce papers.