The owner, Akeem Ajimotokan, worked in the procurement office at Columbia University. He was the original owner of the car, and he was asking $46,000.

The prospective buyer, identified on a bill of sale found inside the BMW as Barion A. Blake, was an ex-convict with previous arrests for stealing BMWs. He apparently had a different price in mind.

After a series of events that included a police car chase and a collision with a yellow cab, the BMW was found in Upper Manhattan on Wednesday morning, its front end crushed. Mr. Blake, who the police believe was driving the BMW at the time of the collision, was gone, but the police officers examining the wreck found Mr. Ajimotokan.

He was in the trunk — alive, barely, though he was bound, with multiple stab wounds and with his ear partially severed.

Mr. Ajimotokan, 33, was taken to Harlem Hospital, where he was listed in critical condition, was placed on a ventilator and was in a coma on Thursday, the police said. Meanwhile, an all-out search was on for Mr. Blake, 30, who had been released from jail in April after serving time in New Jersey for assault, said Paul J. Browne, the Police Department’s chief spokesman.

“The motive appears to be the robbery of a high-end car,” Mr. Browne said.

But many investigative gaps were still being filled in.

It was not immediately clear when Mr. Ajimotokan first placed his ad, with his phone number, on Cars.com; it also was not known when Mr. Blake met Mr. Ajimotokan. But something clearly had gone awry for at least several hours before the accident in Upper Manhattan.

At about 3 a.m., a uniformed officer with the Nassau County Police Department spotted the BMW pulled over on the side of the road, near Jericho Turnpike. The officer saw “two people outside of it,” Mr. Browne said, suggesting that it was Mr. Blake and an accomplice.

“It looks like they are swapping license plates on the vehicle,” Mr. Browne said.

The officer, from the Third Precinct, went to inquire, but the two men jumped in the car and took off westbound on Jericho Turnpike, and then southbound on the Cross Island Parkway, Mr. Browne said. The officer followed the BMW in a marked squad car but lost control on the snow-covered streets, and his car flipped over.

The officer was taken to a hospital for evaluation; a spokeswoman for the Nassau Police Department described his injuries as not life-threatening.

The BMW was next seen in Inwood at 9 a.m. on Wednesday. Witnesses, including the yellow cab driver, said that the suspect tried to drive away after the accident, but that the BMW’s undercarriage got hung up on a concrete divider as he attempted a U-turn at Dyckman Street and 10th Avenue.

When the responding officers from the 34th Precinct looked inside the BMW, they saw several .38-caliber bullets sprinkled in the car’s blood-spattered interior.

The car had only one license plate, affixed to the rear, and the officers had determined that it had been stolen from a 1999 Toyota Camry left in a parking lot in Queens.

They saw that a piece of the rear seat, separating the car’s cabin from its trunk, appeared to be missing. Then they found something worse: Inside the trunk was Mr. Ajimotokan, clinging to life. He was unconscious, having been stabbed several times in the head and body. His hands had been tied behind his back with plastic zip ties.

They found a handwritten bill of sale, dated Jan. 25, to Mr. Blake, of 10th Avenue in Manhattan, from Mr. Ajimotokan. Investigators are examining the possibility that the car was stolen from Mr. Ajimotokan’s home in West New York, N.J. It is unclear if he was assaulted there or at some later point.

“We have reason to believe the individual who ran from the car, or fled the scene, is the same one as the purported buyer,” Mr. Browne said. “Right now, we are working on the investigative premise that Mr. Ajimotokan was lured to some location on the belief there was going to be a purchase of the vehicle and was instead assaulted and put in the trunk and the car stolen.”

Linda M. Foglia, a spokeswoman for the New York State Department of Correctional Services, said that Mr. Blake has also used the alias Adrian Burnett, and has been convicted under both names. Under his alias, Mr. Blake was convicted in February 2001 for four crimes between June 1999 and July 2000, in Nassau County, Manhattan and Queens.

“At one point, he stole a 2000 BMW car, valued at $80,000,” Ms. Foglia said. “Then, he possessed a stolen 2001 BMW.”

Another time, she said, he stole “another BMW worth $79,000.”

In October 2004, Mr. Blake, 6-foot-7 and 215 pounds, was released into the custody of New Jersey authorities.

He returned to the New York State correctional system on Feb. 2, 2007, to serve two to four years for a second-degree assault on a police officer stemming from an episode in April 2006 in Queens, Ms. Foglia said.

No one at Mr. Ajimotokan’s residence could immediately be reached by phone.

Robert Hornsby, a spokesman at Columbia University, where Mr. Ajimotokan is employed, said the university did not comment on police investigations.

“Because of the police situation on this, we don’t ever comment,” he said. “If there is additional information, it would have to come from the N.Y.P.D. first.”