(CNN) The Chicago police officer who killed Quintonio LeGrier has filed a lawsuit against the teen's estate.

In a counterclaim filed last week, Officer Robert Rialmo alleges the 19-year-old whom he shot dead the day after Christmas assaulted him with a baseball bat and caused him to suffer trauma. He's seeking more than $10 million in punitive damages from LeGrier's estate.

Authorities have said LeGrier died from multiple gunshot wounds after the December 26 shooting. A neighbor, Bettie Jones, 55, was also killed. Police have described Jones as a victim who was "accidentally struck and tragically killed." They've described LeGrier as a "combative subject."

Father: No one helped my son after he was shot by cops

Father: No one helped my son after he was shot by cops 07:59

Father: No one helped my son after he was shot by cops

The officer's lawsuit says Jones' death was LeGrier's fault, not his.

"The fact that LeGrier's actions had forced Officer Rialmo to end LeGrier's life, and to accidentally take the innocent life of Bettie Jones, has caused, and will continue to cause, Officer Rialmo to suffer extreme emotional trauma," the lawsuit says.

The lawsuit provides the officer's moment-by-moment explanation of the incident, stating that the teen swung a baseball bat at him twice, barely missing both times.

The officer had his gun holstered and backed up as he shouted orders for LeGrier to drop the bat, the court document says. It was only after LeGrier continued his approach and ignored the officer's commands that Rialmo opened fire, according to the lawsuit.

Making a point

The shooting came as Chicago officials were in hot water for what critics have called a police culture of "shoot first and ask questions later." As details about the case emerged, Mayor Rahm Emanuel said there were "serious questions" about what happened and ordered changes in how city police officers are trained to handle calls involving people who may have mental health problems.

Rialmo's lawsuit gives the officer's side in the controversial case, saying the officer opened fire after LeGrier "took a full swing" at his head, "missing it by inches."

"He told me that he felt the breeze of the bat passing in front of his face, it was that close," attorney Joel Brodsky told CNN affiliate WBBM-TV.

In a statement on Facebook, Brodsky said Rialmo "was taken aback by the speed in which the family of Mr. LeGrier rushed to file a lawsuit."

"He wants to make the point that having a relative killed in an officer-involved shooting is not the same thing as winning the lottery," Brodsky said. "Only the few cases of truly excessive use and abuse of force should be subject to legal actions."

Attorney for estate: Officer is 'trying to deflect'

Bill Foutris, an attorney who represents LeGrier's estate and the 19-year-old's father, said he had a good reason to file a lawsuit against the city quickly: preserving evidence.

"As a result of filing the lawsuit quickly we have gotten well over 40 DVDs of evidence, including police cams and police reports -- all things we would not have had if the suit was not filed when it was," he said. "It would have taken six months to get some of that evidence."

The officer, Foutris said, is trying to steer the conversation away from what happened that day.

"This counterclaim is an attempt to deflect from what the officer did," Foutris said. "He shot a teen four times in the back."

Differing accounts

Chicago's Independent Police Review Authority is investigating the shooting, which happened after officers responded to 911 calls from LeGrier and his father asking for help.

Rialmo's account of what happened contrasts with descriptions in the lawsuits filed by the LeGrier and Jones families.

Antonio LeGrier told CNN he called police after he heard his son banging with a baseball bat on his bedroom door. The father told the Chicago Sun-Times that his son had been prescribed medication for emotional problems.

"I wanted someone to try to help him with whatever he was going through," he said, "because I was not trained."

After he arrived at the apartment in response to a dispatch call of a domestic disturbance, Rialmo said Quintonio LeGrier swung a bat at his head multiple times when they were several feet apart. The lawsuit says LeGrier repeatedly ignored Rialmo's orders to drop the bat.

Eventually, the lawsuit says, "Officer Rialmo reasonably believed that if he did not use deadly force against LeGrier, that LeGrier would kill him."

The officer didn't see Jones, his attorney says "because the sight of her was blocked by Mr. LeGrier, who was standing over the officer about to crack his head open with a bat."