Demi Cuccia

PITTSBURGH — An ex-boyfriend who fatally stabbed a 16-year-old cheerleader started looking for an excuse — mood swings caused by pimple medicine — while still hospitalized with injuries he suffered when he slashed his own throat moments after the killing, a prosecutor said Tuesday at the start of his trial.

John Mullarkey, now 20, is charged with criminal homicide in the Aug. 15, 2007, death of Demi Cuccia, the younger sister of a close friend of Mullarkey's who had been his on-again, off-again girlfriend.

Mullarkey stabbed Cuccia 16 times, mostly in the upper left chest, arm and shoulder, with a 3.5-inch folding knife and then slashed a 10-inch gash across his throat, Allegheny County Deputy District Attorney Mark Tranquilli said.

Mullarkey, of Monroeville, a suburb about 15 miles east of Pittsburgh, essentially spelled out the defense he'll use at trial when he used an eraser board to communicate with a county homicide detective while lying in the hospital days after the crime, Tranquilli told the jury in his opening statement.

"If I did something — no, erase that — if somebody did something bad and they were taking medication, would that be a defense?" Tranquilli said Mullarkey wrote that day.

Mullarkey's defense attorney, Robert Stewart, contends the defendant started taking Accutane about four months before the crime.

Accutane is prescribed as an acne drug of last resort because the U.S. Food and Drug Administration has linked it to episodes of suicide and depression.

Stewart stopped short of blaming the stabbing on the drug, but he said he'll present evidence that Mullarkey had told friends he was concerned about the drug's effect on his moods, among other things. Stewart contends Mullarkey went to Cuccia's town house to reconcile with her and had the knife with him only because he's an avid hunter who has carried it since he was a Boy Scout.

That's important because the issue at trial isn't whether Mullarkey stabbed Cuccia but what his frame of mind was at the time.

Criminal homicide is a generic charge from which the jury can reach a variety of verdicts, including first-degree, or premeditated, murder. Under Pennsylvania law, "premeditation" isn't defined as plotting but rather as a realization — however momentary — that one's actions could kill someone.

Tranquilli says just stabbing Cuccia 16 times is evidence of premeditation. He said that the cheerleader bled to death from a shoulder wound and that some wounds were so vicious they were deeper than the blade's length.

"Somewhere along the continuum of 16 stabs you decide to murder someone," Tranquilli said.

Stewart suggested to the jury that third-degree murder, a killing with malice but no premeditation, or voluntary manslaughter, a killing in the heat of passion, would be more appropriate verdicts.

The trial is expected to last about two days.