A teenage boy fatally attacked a man after the teen’s younger sister told her brother that she was sexually assaulted by the man on a public bus in Utah — an incident that investigators say never happened, according to reports.

Police say the 16-year-old girl told her 17-year-old brother that she was sexually assaulted aboard a Cache Valley Transit District bus around 3 p.m. April 23, the Salt Lake Tribune reported.

The brother immediately sprang into action and tracked down 62-year-old Michael Fife — the man his sister accused — as the man was exiting the bus in the city of Logan, according to the news outlet.

The teen then attacked Fife, who suffered head injuries and was beaten unconscious.

Fife fell to the ground and was left lying on the sidewalk as the teenage boy fled, according to the Salt Lake Tribune.

Later that night, the boy’s sister reported the sexual assault to police, who discovered that surveillance footage from the bus showed that the assault never happened.

“Logan Police detectives reviewed the video footage of the alleged assault,” authorities said, according to the news outlet. “The video showed Mr. Fife walking past the girl, but no sexual assault occurred.”

Fife died from his injuries four days after the attack.

The identities of the teen brother and his sister were not released because of their ages.

The Cache County Attorney’s Office is also investigating the case.