After gunning down his wife and her suspected lover, John Lang was remarkably calm.

The Pitcairn volunteer firefighter dialed 911 and told a dispatcher what he had done, then later told the same to investigators.

"He was very stoic, task-oriented," Monroeville Assistant Police Chief Doug Cole testified yesterday at the first day of Mr. Lang's trial.

"He was very matter-of-fact."

Mr. Lang, 35, is charged with killing Tracy Braverman-Lang and Louis Goldenson, who was a childhood friend to both husband and wife.

He came upon them in the early-morning hours of March 15 in the parking lot of Don Pablo's Mexican restaurant in Monroeville, where he told investigators he saw them embracing and kissing.

"I just shot and killed my wife and the man she was cheating on me with," Mr. Lang explained in the 911 call, played yesterday for the jury.

"Shot and killed them both."

Defense attorney Bob Foreman is arguing that the calm shows his client is not a premeditated killer. Mr. Lang committed a crime of passion, Mr. Foreman said in his opening statement, and he is asking the jury to come back with a verdict of voluntary manslaughter.

Deputy District Attorney Bruce Beemer, meanwhile, pressed for first-degree murder, which comes with a mandatory sentence of life in prison.

He pointed out that Mr. Lang shot his wife and Mr. Goldenson twice in the chest, then parked his car, got out, and shot each of them twice more -- once in the head and once in the chest. When asked by police why he made a second pass, Mr. Lang responded, "Because they weren't dead yet."

Friends testified that the couple, who married in August 2004, had been having relationship troubles. Todd Cain, who said he had known Mr. Lang since they were children, testified that he had seen the two of them get into arguments.

Mr. Cain said Ms. Braverman-Lang taunted her husband frequently for his failure to hold a steady job.

But Mr. Cain testified that Ms. Braverman-Lang and Mr. Goldenson were close friends and nothing more.

The night of the killing, Ms. Braverman-Lang called Mr. Lang to tell him that she was at Don Pablo's with friend Sabrina Orlansky, consoling her because Ms. Orlansky had just learned she had cancer.

Mr. Lang told police he was suspicious because his wife didn't seem upset. Restless and unable to sleep, he went out.

In a compartment next to the driver's seat was a .40-caliber semiautomatic handgun, which Mr. Lang told police he kept for protection when he delivered newspapers in dangerous neighborhoods.

In the Don Pablo's parking lot, he pulled up to Ms. Braverman-Lang and Mr. Goldenson and rolled down the window.

"Hi," he said. Then Mr. Lang pulled out his gun.

The prosecution is scheduled to continue its case against Mr. Lang today.