Police in the UK are on the hunt for a paranoid schizophrenic who failed to return to a psychiatric hospital, where he has been held after being convicted of fatally stabbing his son-in-law more than 20 times, according to reports.

Peter Atkins, 66, was allowed to leave the Kneesworth House Hospital in Bassingbourn, Cambridgeshire, on Thursday so he could visit a Tesco supermarket, according to Sky News.

Atkins was convicted of manslaughter after killing his pregnant daughter’s husband, Stephen Provoost, in 2001. He was sentenced to an indefinite term at the hospital under the Mental Health Act.

Police said Atkins is on twice-daily medication for his condition, and could become aggressive if he does not take it.

“For Peter to not return from free time is out of character,” Detective Inspector Dave Savill said.

“We know he was seen withdrawing cash at Royston Tesco at 2:10 p.m. and then traveled to Royston town center by bus, getting off outside Morrisons supermarket in Baldock Street,” he said.

“It is very important for anyone who believes they may have seen Peter to contact us as a matter of urgency.”

The public was warned not to approach Atkins due to his “unpredictable nature.” Police believe he has ties to south Wales.

Atkins had burst into the couple’s bedroom and stabbed his daughter’s husband of eight months more than 20 times with a knife.

Judge John Griffith Williams called the killing “mind-chilling,” adding that “the memory of a sustained attack on your daughter’s husband will haunt her for the rest of her life,” according to The Sun.