Media playback is unsupported on your device Media caption 'Why did you kill my son?'

University police in the US state of Georgia have shot and killed an LGBT student activist, sparking an inquiry.

Police encountered Scout Schultz, 21, outside a campus dormitory in Atlanta after a call about "a person with a knife and a gun" late on Saturday.

Video shows Schultz refusing to obey police commands, and advancing on them. A family lawyer said Schultz was holding a closed multi-tool.

The student's parents said police should not have used lethal force.

"Why did you have to shoot?" the victim's father said at an emotional news conference on Monday. "That's the question, I mean that's the only question that matters right now. Why did you kill my son?"

What happened to Schultz?

In a video filmed by a fellow student at the Georgia Institute of Technology, Schultz is pictured outside the entrance to a parking garage and can be heard saying "Shoot me!" several times while walking towards the officers.

"Drop the knife, man, come on," a police officer responds.

"Nobody wants to hurt you," another says, before one officer eventually opens fire, hitting Schultz in the chest.

Schultz did not appear to be holding a gun, investigators said, despite what had initially been reported to police.

The computer engineering student from Lilburn, Georgia, was transported to the Grady Memorial Hospital, later dying from injuries sustained in the shooting, the Georgia Bureau of Investigation (GBI) said.

Image copyright Facebook GT Progressive Student Alliance Image caption Schultz's mother noted that the engineering student (pictured) was very active on campus

Why did police open fire?

Police in the US are permitted - and often required - to use lethal force against any suspect who they believe presents an immediate danger to officers or members of the community.

Officers must have a "reasonable belief" that an individual is capable of committing violence, in order to fire on them.

Exact figures for police shootings vary widely, since police forces are not required to submit incidents to the FBI for data collection.

But according to the Washington Post, which tracks civilian deaths at the hands of police, nearly 1,000 people were killed across the country in 2015.

No police officers from the Georgia Tech Police Department (GTPD) were injured in Saturday night's incident, the schools' police force has said. The officer who opened fire has not been named.

Georgia Tech's campus police do not carry Tasers, but are equipped with pepper spray.

School representatives say it was probably the first on-campus police shooting in the past 20 years, if ever.

Who was Scout Schultz?

Schultz - who identified as intersex and preferred to be referred to by the pronoun "they" - was the president of the Pride Alliance at Georgia Tech, and was politically active in progressive causes.

"We are all deeply saddened by what has occurred," the group said in a statement.

"They have been the driving force behind Pride Alliance for the past two years," the group said. "They pushed us to do more events and a larger variety [of] events."

Schultz's mother Lynne said Scout had numerous medical issues, suffered from depression and had attempted suicide two years ago.

"Why didn't they [police] use some nonlethal force, like pepper spray or Tasers?" she told the Atlanta Journal-Constitution.

Image copyright Facebook Image caption Scout Schultz was the president of the Pride Alliance at the Georgia Institute of Technology

What reaction has there been?

A lawyer for Schultz's parents, Chris Stewart, said the blade on the folding multi-tool that Schultz was allegedly holding was not open, and noted that it appears in the video that Schultz never ran towards police.

"I just don't understand how they couldn't have Tasers," Mr Stewart said, adding that he thinks Schultz was "having a mental breakdown and didn't know what to do".

The student's parents William and Lynne Schultz said that they were performing well in school, but suggested that their school workload may have contributed to their mental condition.

Mr Stewart added: "People just breakdown. That's doesn't mean they deserve to die."

"The area was secured. There was no one around at risk," the lawyer said, questioning whether the university police had received sufficient training to deal with suspects with mental health issues.

Georgia Tech said it was "deeply saddened" by what had happened.