A leading gun control group has sued the makers and sellers of the so-called bump stock - a device that enabled the Las Vegas killer to fire his semiautomatic weapons as if they were fully automatic.

In the aftermath of the attack that left 58 people dead and more than 500 injured, police and witnesses spoke of the speed with which Stephen Paddock was able to discharge his weapons. Video footage that captured the sound of the volley of fire, led some to speculate Paddock had an automatic weapon.

It subsequently emerged that in the ten minutes the 64-year-old fired at crowds of people attending a country music festival, he was making use of a bump stock. Bump stocks are legal devices that allow users to mimic the speed of fire of an automatic weapon, of up to 800 rounds per minute.

“This horrific assault would not and could not have occurred, with a conventional handgun, rifle, or shotgun, of the sort used by law-abiding responsible gun owners for hunting or self-defence,” says the lawsuit filed by the Brady Campaign to Prevent Gun Violence.

The suit was was filed last Friday in Clark County District Court in Nevada; it has three named plaintiffs, all victims of the shooting, and seeks class-action status. The lawsuit seeks unspecified damages as well as funds to pay for the victims’ counselling and treatment for emotional distress.

It claims that Slide Fire Solutions, the Texas-based company considered to be the leading manufacturer of the devices, misled federal authorities about their intended purpose and marketed them to thrill-seeking gun enthusiasts.

Las Vegas shooting – in pictures Show all 15 1 /15 Las Vegas shooting – in pictures Las Vegas shooting – in pictures People scramble for shelter at the Route 91 Harvest country music festival after gun fire was heard Getty Las Vegas shooting – in pictures People carry a person at the Route 91 Harvest country music festival after shots were fired David Becker/Getty Las Vegas shooting – in pictures People run from the Route 91 Harvest country music festival after gun fire was heard David Becker/Getty Las Vegas shooting – in pictures A handout photo released via Twitter by Eiki Hrafnsson (@EirikurH) showing concertgoers running away from the scene (C) after shots range out at the Route 91 Harvest festival on Las Vegas Boulevard EPA/Eiki Hrafnsson Las Vegas shooting – in pictures People lie on the ground at the Route 91 Harvest country music festival after hearing gun fire Getty Las Vegas shooting – in pictures A man in a wheelchair is taken away from the Route 91 Harvest country music festival after hearing gun fire David Becker/Getty Las Vegas shooting – in pictures People stand on the street outside the Mandalay Bay hotel near the scene of the Route 91 Harvest festival on Las Vegas Boulevard EPA/Paul Buck Las Vegas shooting – in pictures FBI agents confer in front of the Tropicana hotel-casino after a mass shooting during a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Las Vegas police run by a banner on the fence at the Route 91 Harvest country music festival grounds after shots were fired David Becker/Getty Las Vegas shooting – in pictures An injured person is tended to in the intersection of Tropicana Ave. and Las Vegas Boulevard after a mass shooting at a country music festival Ethan Miller/Getty Las Vegas shooting – in pictures Metro Police officers pass by the front of the Tropicana hotel-casino after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip AP/John Locher Las Vegas shooting – in pictures A cowboy hat lays in the street after shots were fired near a country music festival in Las Vegas Getty Las Vegas shooting – in pictures Las Vegas Metro Police and medical workers stage in the intersection of Tropicana Avenue and Las Vegas Boulevard South after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Sheriff Joe Lombardo (2-R) speaking during a press briefing in the aftermath of the active shooter incident on Las Vegas Boulevard EPA

“The people who attended the concert have suffered so much already. The physical injuries are staggering, and we know the emotional injuries can be equally severe and long term,” the Brady Campaign's co-presidents, Kristin Brown and Avery Gardiner, said in a statement.

Slide Fire Solutions has yet to respond to the allegations.

The filing of the lawsuit came as it emerged Paddock opened fire on a security guard a full six minutes before he launched his attack on attendees at a music festival - a dramatic change to the massacre’s timeline that will likely raise questions about the timeliness of the police’s response.

NRA says nothing could have stopped Las Vegas massacre

Officials said last week that security guard Jesus Campos had approached Stephen Paddock’s room on the 32nd Floor of the Mandalay Bay casino and hotel while the shooting spree was underway.

Police said after Paddock shot and injured Mr Campos - shooting him through the hotel door - the killer did not fire any more shots at the crowd of 22,000 people fleeing in terror.

But Clark County Sheriff Joseph Lombardo has now said that Mr Campos was shot and injured at 9.59pm, six minutes minutes before Paddock embarked on spree using one or more modified semi-automatic weapons.

The massacre sparked a debate about gun control (Getty)

The change in the timing of the events that played out ten days ago on the Las Vegas Strip will likely draw fresh scrutiny about the behaviour of the police and their response to events. Officers have said Paddock was found dead in his room - his life taken by his own hand - when Swat officers stormed his corner suite.

“As I have conveyed to you from the very beginning – and your zest for information and my zest to ensure the public”s safety, and the calming of their minds – is some things are going to change,” Mr Larboardo told reporters on Monday evening, according to CNN. “Now, they are minute changes.”

He added: “In coordination with the FBI’s behavioural analysis unit, a comprehensive picture is being drawn as to the suspect’s mental state and currently we do not believe there is one particular event in the suspect’s life for us to key on.”

More than a week after the killing, police appear little closer to determining what motivated Paddock to open fire on the Route 91 Harvest Music Festival, headlined by Jason Aldean.