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.

PORTLAND — 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 in late 2009.

The court documents confirmed a report Sunday by The Oregonian newspaper about allegations that Terri Horman had sought to have someone kill her husband several months before Kyron Horman's June 4 disappearance.

Investigators have not named Terri Horman as suspect or a person of interest, but in recent weeks they have focused their investigation on her. They distributed flyers asking for information on her whereabouts the day the boy vanished, and twice administered lie detector tests.

A call to Terri Horman's lawyer was not immediately returned Thursday.

Police have said she was the last known person to see the boy. She told police she left him at his school, about two miles away from their home, after an early morning science fair.

A former teacher and ex-bodybuilder, Terri Horman had become increasingly isolated from family members.

Kaine and Kyron Harmon's birth mother, Desiree Young, have issued appeals to Terri Horman to cooperate with investigators.

Late last month, Kaine Horman moved out of the couple's home in the countryside west of downtown Portland, filed for divorce and got a restraining order against his wife — including a provision that she not have access to firearms or ammunition.

That restraining order was unsealed by a judge on Thursday, following requests by a coalition of news organizations, including The Associated Press, that it be made public.

The restraining order contained the first publicly released suspicion by Kaine Horman that his wife was connected to Kyron Horman's disappearance.

"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."

His statement contained no details on how Terri Horman might be involved in the boy's disappearance.

The sheriff's office has refused to confirm details of the alleged murder-for-hire plot and did so again Thursday. 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, who is now living with Kaine Horman. Terri Horman also has a teenage son from the first of two previous marriages.

The investigation has become one of the most intense in recent Oregon history, and has attracted national attention.

At the start of the search, Terri Horman organized friends to pass out flyers. She also appeared at two press conferences, along with Kaine Horman, the boy's mother, Desiree Young of Medford, and her husband, Tony. She has not appeared at press conferences since.

Terri Horman was married twice before marrying Kaine Horman in April 2007. Information on her Facebook page, since blocked, described her hometown as Roseburg.

Kaine Horman, who divorced from Desiree Young in 2003, works for chipmaker Intel at its suburban campus in Hillsboro.