Joseph Vincent Giongo, who pleaded guilty in March to beating and stomping his wife to death in front of their 7-year-old son in their Conshohocken home in December 2007, was found guilty but mentally ill Monday.

Doctors for the prosecution and defense agreed in a Montgomery County Court hearing that Giongo, 46, suffered from severe depression and psychosis, and that his illness played a role in his fatal attack on Bernadette Giongo, 42. Prosecutors said the attack started when Joseph Giongo got angry over the cost of a takeout-food order.

The couple's three sons, ages 7, 10, and 17 at the time of the slaying, have been staying with a grandmother since then, Assistant District Attorney Wallis Brooks said.

Giongo had been found unfit to stand trial in April 2008 and was sent to Norristown State Hospital for treatment. He was cleared to face the charges a year later.

He faces a maximum penalty of 20 to 40 years confinement for the conviction of third-degree murder. Judge Kent H. Albright's finding that Giongo was mentally ill means part of that sentence could be served in a mental institution.

Sentencing is scheduled for September.

Contact staff writer Derrick Nunnally at 610-313-8212 or dnunnally@phillynews.com.