After 45 minutes of deliberation, an Allegheny County jury this afternoon convicted a Monroeville man of first-degree murder for stabbing his off-and-on girlfriend to death.

The verdict against John Mullarkey, 20, was a rejection of the Accutane defense offered by defense attorney Robert E. Stewart, who argued that Mr. Mullarkey could not form the intent to kill Demi Cuccia, 16, a Gateway High School cheerleader, partially because he had recently stopped using the acne medication.

Mr. Mullarkey, who was stone-faced as the verdict was read, was sentenced immediately to life in prison without the possibility of parole by Common Pleas Judge Jeffrey A. Manning and declined an opportunity to speak on his own behalf. Mr. Stewart said he advised his client not to speak because he will appeal the verdict.

Mr. Stewart unsuccessfully asked for a mistrial this morning because of new evidence -- Accutane has just been pulled from the market.

Judge Manning denied the motion because Roche Pharmaceuticals, in announcing the decision Friday, said they pulled the drug for economic reasons. The market share of Accutane has waned in recent years as generic versions have become available, the company said, also citing expensive lawsuits filed against the company based on Accutane's side effects.

Because the company didn't say it was yanking the drug for safety reasons, Judge Manning said it didn't have a significant impact on the case.

"It's a coincidence, more than anything else," Judge Manning said.

The judge allowed the case to proceed with closing arguments.

Mr. Stewart said that Mr. Mullarkey was an impulsive teen whose mind was in a tempest over the failing relationship with Demi.

Mr. Stewart asked jurors not to convict his client of first-degree murder -- which carried a guaranteed life sentence -- because he didn't go over to her house Aug. 15, 2007, with the intention of hurting anyone, but ended up stabbing Demi to death and slitting his own throat in a suicide attempt. Part of Mr. Stewart's "diminished capacity" defense was that Mr. Mullarkey was depressed after recently quitting Accutane, which has been blamed for instances of suicide and depression -- though not definitively linked.

Mr. Stewart described Mr. Mullarkey as "a scared, a confused and an upset 18-year-old boy that went over there with an intention of being with a girl he loved."

In his closing, Deputy District Attorney Mark V. Tranquilli pointed out that the premeditation necessary for first-degree murder can form quickly, and he ended by banging his fist on a ledge in front of the jury box 16 times -- one for each stab wound Demi suffered -- and asking when along the way did he form the intent to kill.

"All this nonsense about Accutane -- the Boogeyman -- and diminished capacity," Mr. Tranquilli said, "that's a bunch of malarkey."