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 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 fliers 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.

Kyron’s birth mother, Desiree Young, and Kaine Horman 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.