EXETER, N.H. — A high-school student spent his 17th birthday on the witness stand Tuesday tearfully testifying that his teacher-lover goaded him into shooting her husband to death.

“I said, `God forgive me’ … I pulled the trigger,” William Flynn recalled as he detailed how he and a high-school friend ransacked Pamela and Gregory Smart’s condominium to make it look burglarized, then waited for Smart to return home.

The date was May 1, one week before the Smarts’ first wedding anniversary.

Tuesday was Flynn’s second day on the stand at the murder-conspiracy and accomplice-to-murder trial of Mrs. Smart, 23, media coordinator at Flynn’s high school in Hampton.

Flynn testified Monday that Mrs. Smart seduced him and then coaxed him into killing her 24-year-old husband because a divorce would leave her with nothing. According to Flynn, Mrs. Smart said her husband’s death would mean an insurance settlement and then she and Flynn could have a life together.

“I didn’t kill Greg for Pam. I killed to be with Pam, because Pam threatened to break up with me,” Flynn said.

“Whatever she told you to do, you would do?” Mrs. Smart’s defense lawyer, Mark Sisti, asked.

“Yes. I probably would do it,” Flynn replied.

“It was like you had no brain?”

“I had a brain,” Flynn said, “but I was in love.”

Sobbing at times and wiping tears from his face, Flynn testified about waiting inside the Smarts’ Derry condo for the young insurance salesman to return home. He said he and Patrick Randall, now 17, discussed whether to slash Smart’s throat with a knife from the kitchen or knock him unconscious with a candlestick.

A third teen-ager, Vance Lattime, waited in a getaway car he had borrowed from his grandmother, Flynn said.

Randall testified last week that he was supposed to stab Smart, but couldn’t bring himself to do it with the victim on his knees begging not to be hurt.

Flynn testified Tuesday that he then took out a .38-caliber pistol loaded with hollow-point bullets he had bought with money from Mrs. Smart. He said he put the gun close to the back of Smart’s head and paused for what seemed like a hundred years.

He then asked forgiveness and pulled the trigger, he said, his voice breaking with emotion.

Flynn told prosecutor Paul Maggiotto he was a reluctant witness.

“I didn’t want to testify against Pam,” he said. “I told her I’d never tell on her.

“I loved her.”

He also said he didn’t want to kill Smart.

“I wanted to be with Pam, and that’s what I had to do to be with Pam,” he said.

Prosecutors claim Mrs. Smart used her emotional control over Flynn to get him to murder her husband. The defense contends that Flynn and his friends are thrill-killers who killed Smart on their own, then framed his widow to avoid mandatory life-without-parole prison terms.

Flynn and two friends, all Seabrook residents, face 18- to 28-year prison terms in a plea-bargain requiring them to testify against Mrs. Smart.

Flynn said he met her in a program designed to keep young people from drugs and alcohol. He also took part in a student video project she ran.

He testified that he was still 15 early last year when Mrs. Smart summoned him to her office and nervously told him she thought about him all the time.

Flynn, a thin youth with longish dark hair, said that when they first had sex about 10 days later, they listened to heavy metal rock and made love, re-enacting a scene from “9 1/2 Weeks,” a sexually explicit and psychologically sadistic movie.

He said it was the first time he had sex, and said they made love “everywhere … on the bed, on the floor.”

Later, he said, they met for trysts at each other’s houses, the beach and parking lots.