COLUMBIA, Mo. -

The man charged with killing a fellow patient at Columbia's VA hospital told a Boone County judge he is not guilty Monday.

Rudy Perez is accused of beating Robert Hill to death in a common room inside the veteran's hospital Feb. 1.

Defense attorney David Smith said Perez suffers from schizophrenia and was off his medications during the incident.

This type of plea puts the burden on Smith to show Perez suffered from a mental disease or defect.

Smith wouldn't go into details.

"We're investigating and we're going through a lot of things so we don't to say too much at this point," Smith told ABC 17 News.

Prosecuting Attorney Dan Knight told ABC 17 News he has not decided whether he will seek the death penalty.

"I've been in contact with victim Robert Hill's son and that family of course is very saddened about what has happened. We're going to do everything we can to achieve justice in the case," Knight said.

Perez is now awaiting his next court date, which has not been set yet.

A trial judge still needs to be assigned.