Police Said Driver Was Shot Lunging at Officer. Video Shows Otherwise.

The initial account on Monday afternoon of how a Philadelphia police officer had fatally shot a 27-year-old man was straightforward: After a brief car chase, a man wielding a knife got out of his car and lunged at the officer, who shot and killed him, police said at the scene, according to local press reports.

But at a news conference on Wednesday, top police officials gave a very different account. According to body camera footage, the officials said, the man was still in his car when the officer shot him.

“I understand and want to acknowledge the hurt and confusion that family and community members can experience when details of investigations change, and especially when they change in a very public way,” Danielle M. Outlaw, the Philadelphia police commissioner, said. “I also understand that the information I’m about to provide will raise additional questions,” she added.

The police have not named the person who was killed. However, family members identified him as Eddie Irizarry, 27, a quiet and withdrawn man who, they said, liked to tinker with motorcycles and was being treated for serious mental illness, including schizophrenia. “He didn’t have problems with anybody,” his sister, Maria Irizarry, said in an interview. She said that her brother, who had moved to Philadelphia about seven years ago from Puerto Rico, did not understand English.

In the news conference, Ms. Outlaw provided the following account of what the department now says occurred: Shortly after noon on Monday, two officers were sitting in a marked police car when they saw a Toyota Corolla driving erratically in the Kensington neighborhood in northern Philadelphia. The officers, whose names have not been released by the department, followed the car as it turned the wrong way down a one-way street and watched it pull into a parking spot midway down the block.

The officers approached the car from different sides. The officer on the passenger side tried to open the door, then alerted the officer on the driver’s side that the man in the car had a weapon, Ms. Outlaw said. The officer on the driver’s side then fired “multiple times into the vehicle,” killing the man.

At the same news conference, Peter Marrero, a detective who is investigating the shooting, said that two knives were found in the car: a “kitchen-style knife” and a “a serrated folding knife.” Ms. Irizarry said that her brother did carry a pocketknife everywhere he went but “always as a tool, not as a weapon.”

At the scene of the shooting on Monday, a police spokeswoman told reporters that the driver had initially fled from officers and that after he stopped, he got out of the car with his knife and ignored commands for him to drop it. He then “lunged” at the officers before one of them shot him, she added.

None of that account appears to be true.

At the news conference on Wednesday, the chief of detectives, Christine Coulter, said that version of events was “something that was called into police radio.” She said that on Tuesday, once the department’s Officer Involved Shooting Investigation Unit had looked at body camera footage, officials realized that the initial account was wrong. The footage has not been made public.

“I understand folks not really being sure whether or not they should even trust what we’re saying today because of what we said initially,” Ms. Outlaw said. “But I’m hoping that they see that this is a genuine effort to do everything that we can to share what we know when we have it.”

Officials said the shooting was being investigated by the police internal affairs unit to determine whether the officers followed department policy and by the district attorney’s office to determine whether a crime had been committed. Police said that both offices were equipped with Tasers at the time of the shooting. The officer who fired the fatal shots has so far been identified only as a “five-year veteran” of the department; under department policy, an officer’s name is released within 72 hours of a shooting.

According to the department’s statistics, there have been two other “officer involved shootings” this year, neither of them fatal. There were 15 such shootings last year, five of them fatal.

None of this is comfort to Mr. Irizarry’s family members, who said they had obtained a lawyer.

“They changed the story and they keep changing the story,” his aunt, Zoraida Garcia, said on her way to make funeral arrangements. “What they’re saying are lies. What the police did to my nephew was an abuse.”

Ana Facio-Krajcer contributed reporting.