Kyron Horman's Father Serves Stepmom With Divorce Papers

PORTLAND, Ore. (CBS/AP) Speculation about what happened to 7-year-old Kyron Horman, the Oregon boy who went missing from his elementary school June 4, has increasingly focused on Kyron's step-mother and her version of events that led up to the boy's disappearance - and now Kyron's father has walked out on her, taking Kyron's half-sister with him.

PICTURES: Kyron Hormon Missing: New Photos

Court documents show that Kaine Horman filed for divorce from Terri Moulton Horman on Monday, as well as requesting a restraining order against her.

The family had previously shown a united front even as police seemed to be focusing on Terri Horman, pouring through her cell phone records and giving her two polygraph tests.

Police have said she's the last known person to see Kyron Horman alive. After a massive search, the Multnomah County sheriff's office recently described the case as a criminal investigation.

The boy's father told CBS' The Early Show Friday that he believes "[Terri] is committed as the rest of our family is to finding Kyron."

PICTURES: Kyron Hormon Missing: New Photos

But something must have changed over the weekend because on Monday Kaine Horman as well as Kyron's mother Desiree Young and her husband Tony Young issued a statement through the sheriff's office that was signed only "Desiree, Tony and Kaine."

It did not include Terri Horman's name.

In the statement, the three said they have been fully briefed on the investigation and support the sheriff's office.

"Any actions taken by the investigation, or by us, are based on the best interests of Kyron and Kiara and comply with the law," the statement added.

Sheriff's spokeswoman Lt. Mary Lindstrand said Monday night her office is "not talking about personal issues going on with the Hormans." She said Terri Horman is neither a person of interest nor a suspect.

Kyron was reportedly last seen June 4 walking down a hallway toward his second-grade classroom, wearing a "CSI" T-shirt and dark cargo pants. Terri Horman told police that she stayed with him for the science fair before class and then let him walk to his classroom alone. She called police that afternoon when he didn't get off the school bus.

Anyone with information on the whereabouts of Kyron Horman is asked to call the Multnomah County Sheriff's tip line at 503-261-2847.

Complete Coverage: Kyron Horman Missing