The attorney for David Jonathan Brown, the man charged in the December killing of USC Professor Bosco Tjan, said in an interview Wednesday that he will be "looking into the sanity" of his client.

Brown, 28, waived his right to a speedy preliminary trial in a pretrial hearing on Wednesday, agreeing to postpone it until March 21. He faces felony murder charges.

Deputy District Attorney Beth Silverman pointed out that such a "mental state defense" could delay an already lengthy pre-trial process.

Elyn Saks, a USC law professor and expert in criminal law, said that a mental state defense is a high burden to prove.

"You can be very mentally ill, very crazy and not criminally insane," she said.

Another possible defense is that Brown isn't mentally capable of standing trial. Saks said this defense would require the defense to prove Brown cannot consult with his lawyer "with a reasonable degree of rational understanding."

Either case is unlikely; Saks says only one percent of cases even raise an insanity defense–let alone win one.

Brown was a student in Tjan's cognitive neuroimaging lab. Tjan was stabbed to death on Dec. 2.

Helen Demasio, the director of the lab in which Tjan worked, said they "suffered a major loss" with his death, but that they have "significant expertise in the area of neuroimaging within the Center." They have appointed a new co-director and that their work "has continued without interruption and with no loss of quality."

Correction: An earlier version of this article referred to Silverman as the district attorney. She is the deputy district attorney.