As a frantic onlooker and police watched, Benjamin Klinger feigned unconsciousness and smothered the last breaths out of his 17-year-old girlfriend.

Minutes before, Klinger, 19, of Elizabethtown, had intentionally driven into a guard rail on Route 283 at approximately 100 mph, police say.

Chilling, new details about how Samantha Heller was allegedly murdered by her abusive boyfriend emerged Saturday in a press conference and in a police affidavit from the murder case.

In what District Attorney Craig Stedman on Saturday called one of the most complicated cases he's ever seen, Klinger was arrested at his home Friday evening and charged with criminal homicide for the early-morning car crash Dec. 4 in Rapho Township.

After the collision — which police say Klinger had threatened previously — Klinger got out of the undamaged driver's door and went to the passenger side where badly injured Heller was face-down in the grass, her legs still inside the vehicle.

He sat on her head and torso to finish her off, police allege.

A motorist who had come on the scene heard the girl yelling repeatedly, "Get off of me, get off of me!" according to a police affidavit in the case.

Another motorist at the accident scene heard the screaming and called 911. On a recording of that call, the motorist can be heard repeatedly asking the dispatcher if he should move the people.

He is told by the dispatcher not to move Klinger off of Heller, according to the affidavit. "We don't want to move them" and "The help will be coming to move them the right way ... help is being dispatched," the affidavit says.

Two police officers observed Klinger sitting on his girlfriend. They later said Klinger appeared to be "slipping in and out of consciousness" and that he would close his eyes for several seconds, moan, then reopen them without attempting to move.

But Stedman said at a press conference Saturday that Klinger was actually intentionally asphyxiating Heller.

Heller was pronounced dead at the scene.

Dr. Wayne Ross, Lancaster County forensic pathologist, performed an autopsy later that day and ruled Heller's death a homicide. The manner of death "is consistent with someone sitting on the victim," Ross said, according to the affidavit.

Klinger was transported by ambulance to Hershey Medical Center. He was released two days later.

A Hershey employee reported Klinger saying, "I feel guilty. I told her she could lay down in the back seat without a seat belt on and she was pregnant with my child and now she is dead," according to the affidavit.

But reconstruction of the accident by police showed Klinger was not ejected from the vehicle and couldn't have landed on his girlfriend.

Stedman said Klinger had a history of abusing his girlfriend, and this wasn't the first time he had threatened an intentional crash in their two-year "on-again, off-again" relationship that involved physical and mental abuse on Klinger's part.

Approximately 11 months before the crash, a relative told police Heller called her while in a car Klinger was driving.

The relative said she could hear Klinger yelling, "If you don't get off your phone with your (expletive) relatives right now, I'm gonna run this car right off the road and then none of them are gonna ever see either one of us again," according to the affidavit.

A close friend of Heller's told police that the victim had recently confided in her that Klinger had threatened to kill them both in a car crash.

Klinger is a 2011 graduate of Lancaster Mennonite High School. Heller was a senior at McCaskey High School.

In June, Klinger was charged with simple assault for running over Heller's foot with his car. The case had not yet been heard in court.

Klinger is believed to be the first driver in a fatal accident here ever to be charged with homicide, rather than homicide by vehicle.

In addition to the murder charge, Klinger faces nine other charges stemming from the accident, including drug and vehicle violations.

Manheim Borough Police Chief Joseph Stauffer asked people who knew of Klinger and Heller's relationship to call him at 665-2481.