ESTACADA, Ore. — An Oregon father is struggling to try to understand why his adult son allegedly decapitated his mother on Mother's Day and then showed up at a grocery store with her head, stabbing a clerk there until workers overpowered the man and police arrested him.

David Webb said his 36-year-old son, Joshua Lee Webb, had vision problems and received Social Security payments but never showed any signs that he might be capable of the crime. Police described him as "catatonic" after his arrest.

"I never foresaw a problem. If I had I would have stopped it," David Webb told The Associated Press before bursting into sobs during a telephone interview.

BACKGROUND: Man carrying mother's severed head stabs Estacada store worker

Joshua Lee Webb decapitated Tina Marie Webb Sunday afternoon at the family's rural home in the once-significant logging town of Colton, about 40 miles south of Portland, the Clackamas County Sheriff's Office said.

He then showed up at about 12 miles away at a small grocery store, covered in blood with a large kitchen knife and carrying her head, authorities said.

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The mother had told David Webb that she believed their son was depressed, but the father said he never saw any indications of that when he spoke with his son. The parents recently bought him a dog because he wanted one.

"I just can't believe I lost my wife and son in one day...I wish I had some answers, but I don't. I waited all my life to retire with my wife, and now I can't. That's all I know."

An autopsy was performed Monday on Webb, 59. Her son was booked on charges of murder and attempted murder.

After arriving at the store, Joshua Lee Webb stabbed the store employee but was quickly subdued by other employees who held him until officers arrived, authorities said.

The grocery store checkout clerk was hospitalized and expected to survive.

Dubois reported from Portland. Follow Gillian Flaccus at