A video showing the fatal shooting of a 17-year-old girl, Kristiana Coignard, in a police station lobby in Texas has been released by authorities.
According to a Sky news report, the girl is seen scuffling with a policeman shortly before he and another officer fire a number of shots at her.
Police say the girl lunged at an officer with a butcher knife and that a Taser failed to stop her.
“All the patrol officers carry Tasers, plus expandable batons,” Police Chief Don Dingler said.
“I think you’ll see from the video that the time was a factor. There was no time for the officers to use other means.”
The girl’s family say she had mental health problems and have questioned why police had to shoot her.
Miss Coignard was living with her aunt, Heather Robertson, in Longview, eastern Texas.
Ms Robertson said her niece had bipolar disorder and had twice attempted suicide, but was not violent toward anyone except herself.
The video shows Miss Coignard entering the Longview police station. There is no audio, but police spokeswoman Kristie Brian said the girl requested help but would not say why.
Officer Glenn Derr was the first officer to respond. When he approached the teenager, she held up her hand, which had “I have a gun” written on it, Ms Brian said.
The video shows Office Derr struggling with the girl and trying to subdue her. At one point, the officer throws her to the ground.
She is lying on the floor and the officer is kneeling, holding her down. Then he gets up and steps back – according to police, this happened when he saw Miss Coignard reaching for a butcher knife in her waistband.
Two other officers – Gene Duffie and Grace Bagley – arrived at the scene of the confrontation.
The girl is seen charging at Officer Derr. The officer Duffie fired his Taser, and the other two quickly followed with gunshots.
All three officers are on paid administrative leave while the Texas Rangers investigate.