PHILADELPHIA (AP) -- A 13-year-old boy whose body was found in a shallow creek four days after he went missing shot himself in the head with a gun taken from his suburban home, his family said Monday.

Cayman Naib

An autopsy conducted Monday determined that Cayman Naib committed suicide Wednesday after he left his Newtown Square home, the Delaware County medical examiner's office said. Although the gun was fitted for a trigger lock, it was still able to fire, the family said.

"No words can adequately express the Naib family's pain and sadness at this news," the family said in a statement on Facebook.

Cayman left his home Wednesday after receiving a negative school progress report just before a snowstorm and frigid temperatures descended on the Philadelphia area. His disappearance triggered a massive search that involved police, the civil air patrol, the FBI and about 200 volunteers. His snow-covered body was found Sunday in a creek near his family's home.

A Facebook page called "Find Cayman" was used by the family to raise awareness of his disappearance. In the wake of his death, the page was changed to "Celebrating Cayman," as a place for "friends, family, and the community to share their special thoughts, stories, and memories of Cayman."

The family took to the page Monday afternoon to thank those involved with the search.

"(The family's) only solace throughout these past few days has been the closure they have received from the community's efforts to find Cayman," it said.

Funeral arrangements haven't been announced.