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Former NFL star Steve McNair was shot dead in his sleep last week by a 20-year-old girlfriend distraught about mounting financial problems and her belief that he was seeing someone else, police said Wednesday.

Investigators may never know why Kazemi shot McNair four times as he dozed on a sofa early Saturday before turning the gun on herself, Police Chief Ronal Serpas said.

But interviews with friends revealed that she was making payments on two cars, her rent was doubling and she suspected the married McNair was having a second affair with another young woman.

She told a friend on Friday that "My life is a ball of s—- and I should end it," Serpas said.

Police earlier had labeled McNair's death a homicide, but waited for further tests and the revelations about Kazemi's personal problems before concluding that she pulled the trigger in a condominium McNair rented with a friend.

McNair, 36, a quarterback for the Tennessee Titans most of his career, met Kazemi six months ago at a restaurant where she was a waitress and his family often ate. She seemed happy and eager to build a life with him, but something went wrong.

"We do know that she was clearly sending a message during the last five to seven days of her life that things were going bad quickly," Serpas said, though there was no indication she told anyone she planned to harm McNair.

Serpas said detectives learned that Kazemi recently found out about another young woman she thought McNair was romantically involved with and had even followed that woman home, though she did not confront her.

Serpas said police believe McNair was asleep when he was killed because there were no defensive wounds. After shooting McNair in the head, Kazemi apparently shot him twice in the chest before shooting him again in the head and then shooting herself. The gun was found underneath her.

She sat next to his body and tried to position herself to fall into his lap when she died. She did, but her body slid to the floor and ended up at McNair's feet, Serpas said. The gun was found underneath her.

Kazemi's family told reporters that the woman was so confident McNair was divorcing his wife of 12 years that she was preparing to sell her furniture and move in with him.

But associate Mike Mu, who has worked with McNair's charitable association for years, said McNair's wife, Mechelle McNair, "didn't know who this girl is." No records of divorce proceedings have surfaced.

Mechelle McNair, who has not spoken publicly since the shooting, has been described by people close to her as being very upset and distraught. Agent Bus Cook said McNair's wife was "in and out" of it in the hours after the shooting.

Two days before the shooting, police stopped Kazemi driving the Cadillac Escalade sport utility vehicle that McNair had given her for her birthday in May.

According to an arrest affidavit, Kazemi had bloodshot eyes and alcohol on her breath. She refused a breath test and told an officer "she was not drunk, she was high." She was charged with DUI. McNair was with her but not charged. He later made her bail.

Police released video of the DUI stop after they announced Wednesday that Kazemi killed McNair and herself.

In the video, Kazemi repeatedly asks an officer to have McNair come to the window of the police cruiser where she's sitting. The officer responds, "He's not happy." McNair, who wasn't charged, leaves in a cab without coming to talk to her. He later bailed her out.

Kazemi laughs and teases the officer but also says she's scared of going to jail.

Serpas said that even though both her name and McNair's were on the Cadillac's title, she was apparently responsible for making payments. She was also making payments on another car after she couldn't sell it.

Mu is handling media inquiries for Thursday night's memorial service in Nashville. A funeral service will be held Saturday in Mississippi.

Robert Gaddy, the close friend who reported McNair's death to 911 defended his friend since their days playing football at Alcorn State to The Tennessean. Gaddy, who did not immediately return a text message to his cell phone from The Associated Press on Wednesday, said the McNairs' Nashville home was on the market because they were looking for a new house.

"People need to quit talking about what they don't know. Mac never said anything to me about he was going to get a divorce, and ever since this has all happened everybody is trying to paint a certain picture and they need to talk about what they know," Gaddy told the newspaper.

The four-time Pro Bowl quarterback was being remembered Wednesday at the stadium where he played much of his career. The Tennessee Titans opened LP Field for fans to watch video highlights of McNair's 13-year NFL career, look at photos of the quarterback and had a book for them to write messages that will be given to the family.

The McNairs married in 1997, and Mechelle is the mother of two of his four sons. She met McNair while both were students at Alcorn State, though she also studied nursing in Nashville and became a nurse while he played for the Titans.

Mechelle McNair tended his numerous injuries at home, changing bandages and even helping with intravenous fluids in 2001 when her husband needed I.V. antibiotics for an infection that developed after shoulder surgery.