Girlfriend “murdered” her boyfriend, a footballer, in an alleged murder-suicide plot after “relationship betrayal”

Warning: This article contains a discussion of suicide that some readers may find disturbing

There is a brand new volume in the anthology documentary series UNKNOWN, that delves deep into the extremely wild world of sports.

This season focuses on three new stories – one of which is the harrowing tale in which a girlfriend “murders” her footballer boyfriend in an alleged murder-suicide plot after being “betrayed” in their relationship. Watch the official Netflix trailer here:

Steve “Air” McNair was best known for his exciting run to the Super Bowl with the Tennessee Titans, for whom he played from 1993 to 2005.

However, his career ended abruptly in 2009 with his assassination when he was only 36 years old, and to this day many questions surrounding his death remain unanswered.

“People liked him. He smiled, he was quiet,” said Jeff Fisher, McNair's former NFL coach.

“He didn't really like the cameras and interviews, but there was no doubt that he had what it takes to excel at that level.”

The documentary looks back at the shock when Nashville police discovered that the athlete had been murdered on July 4, 2009 as a result of numerous gunshot wounds.

The NFL quarterback was found shot in the head and lying next to him was the body of a 20-year-old woman later identified as Sahel “Jenni” Kazemi, who was McNair's girlfriend at the time.

Although McNair was married, he and Kazemi dated for six months.

“They started to really fall in love with each other, and it was real,” said Emily Andrews, a friend of Kazemi's. “They talked about adopting children together one day and really building a life together.”

A relative of Kazemi added: “She was happy with him. She said he would divorce very soon, in about two weeks.”

Police found that tensions arose in McNair and Kazemi's relationship when she reportedly learned of McNair's infidelity after discovering condoms in the condo they shared.

McNair's then-girlfriend, Sahel “Jenni” Kazemi, was found responsible for both deaths in a murder-suicide case. (Netflix)

“I think he really broke her heart,” Andrews revealed, while Charles Robinson, a detective with the Nashville Police Department, added: “I think everything went downhill after Jenni realized that Steve was seeing other women.”

It also emerged that Kazemi had purchased a pistol just two days before her death, which was found in the apartment where the bodies were found.

An investigation revealed that Kazemi shot him four times and then committed suicide.

However, private investigator Vincent Hill questioned the Nashville police investigation, questioning its nature and whether other suspects should have been questioned.

UNTOLD: The Murder of Air McNair is currently available to stream on Netflix.