COPS scrambling to find a motive for the Las Vegas atrocity may probe whether gun maniac Stephen Paddock had a grudge against a casino.

The gambling addict sued the Cosmopolitan Las Vegas in 2011 after he claimed he “slipped” in the lobby, with CCTV showing the “unkempt” killer collapsing on the floor.

27 Las Vegas gunman Stephen Paddock was filmed falling over at a casino in 2011, sparking a failed compensation bid

He demanded $100,000 (£75,000) to cover medical bills after saying he tore a hamstring and sprained a wrist, but the case was dismissed in 2014.

Investigators may probe whether this incident sparked a chain of events that drove him to carry out the deadliest mass shooting in modern US history.

Paddock sprayed hundreds of rounds of ammo from the 32nd floor of the nearby Mandalay Bay casino and hotel on Sunday night.

He used a terrifying arsenal of 23 weapons to rain a hail of bullets on the crowd at the Route 91 country music festival, killing 59 and wounding more than 500 others.

Detectives are now desperately trying to determine why the seemingly mild mannered ex-accountant carried out the mass shooting.

27 He was filmed strolling through the hallway at the Cosmopolitan Las Vegas before falling down

27 Footage shows him being escorted to a back hallway of the casino where he is seen rubbing his leg

CCTV shows the “slovenly” killer apparently falling over in the hallway of the Cosmopolitan in 2011.

He claimed he slipped on an unknown liquid on the casino floor.

Footage shows him collapsing on the floor and later being escorted to a back hallway of the casino where he is seen rubbing his leg and teetering in front of paramedics.

But the lawsuit was rejected as “without merit” and he was left owing $270 in court fees.

He still reportedly owed this debt when he killed himself on Sunday after the Vegas bloodbath.

27 Stephen Paddock has been named as the shooter responsible for the mass killing in Las Vegas Credit: Twitter

27 Paddock, right, pictured with his brother Eric, left, in 2002 Credit: @WESH

The casino involved in the lawsuit was not the same place Paddock carried out the atrocity.

But the incident sheds more light on the mass murderer who was reportedly hooked on video poker and blew £8,000-a-day in the weeks before the bloodbath.

The multi-millionaire property developer owned two planes, regularly spoke to his family and lived a comfortable life in sleepy Mesquite, rural Nevada.

But he also had a dark side – an obsession with gambling that saw him blow tens of thousands of dollars in Vegas casinos before he killed 59 and wounded more than 500 others.

His brother, Eric, revealed the mass murderer was a “big fish” in the Vegas casinos.

“It's like a job for him. It's a job where you make money,” Eric said.

“He was at the hotel for four months one time. It was like a second home. He’s known. He's a top player. He's the small end of the big fish.”

In the days before the slaughter, Paddock had sometimes gambled more than £22,000 ($30,000) in the Vegas casinos, NBC reported.

27 Paddock is pictured here in his high school yearbook photo in 1971 Credit: The Mega Agency

27 The killer was also on the tennis team at his school Credit: The Mega Agency

27 The Mandalay Bay can be seen behind a police cordon the day after the attack Credit: Reuters

27 Sobbing witnesses comfort each other the day after the massacre Credit: AP:Associated Press

27 Concert-goers hug each other near the scene of the mass shooting Credit: AP:Associated Press

Cops are still "working to process the crime scene from the Mandalay Bay Hotel and also investigate the motives of the shooter".

"Detectives are combing through evidence to uncover the shooter's motives and any other pertinent information that will help shed light on the Sunday night massacre."

Cops yesterday admitted they were not yet sure of the Vegas gunman’s motives, with Clark County Sheriff Joseph Lombardo telling reporters: "We have no idea what his belief system was – I can't get into the mind of a psychopath."

But while the shooter himself had no criminal background, the same reportedly cannot be said for all his family.

Paddock’s father was Benjamin Hoskins Paddock, a serial bank robber.

The bandit is understood to have wound up on the FBI’s Most Wanted list in 1969 when he escaped from prison in Texas while serving a 20-year sentence.

27 The shooter was the son of serial bank robber Benjamin Hoskins Paddock Credit: FBI

27 Paddock's father was on the FBI's Most Wanted list in 1969 Credit: FBI

27 A bloody wheelbarrow used to ferry injured people to safety is seen in the street Credit: EPA

27 Blood-stained clothing lies where it was left on the road during the massacre Credit: EPA

27 The blood of one of the victims is splattered on the ground next to a shoe Credit: EPA

Paddock’s brother Eric also said he was baffled, insisting his sibling had no religious or political affiliations and was just a regular guy who liked to gamble.

Some have pointed to his "high stakes poker playing" for six-figure sums as a potential trigger.

Detectives revealed Stephen carried out tens of thousands of dollars' worth of transactions in the hours leading up to the attack - although they would not say whether they were wins or losses.

"I have absolutely no information he lost a bunch of money", Eric told reporters. "The casino would know that."

It comes after horrifying video showed blood-soaked concert-goers running in terror from the Route 91 country music festival after hundreds of rounds were fired from a nearby Mandalay Bay Resort Casino balcony.

Pictures show two smashed in windows at the luxury resort from where the shooter is believed to have let off a hail of deadly gunfire.

What we know so far:

- At least 59 people are dead and more than 500 are injured, making the attack the worst in US history

- The shooter has been named by police as Stephen Craig Paddock, 64, who was firing from the 32nd floor of the Mandalay Bay Resort Casino, and who was found dead

- Police now believe they have found Marilou Danley, 62, a woman believed to have been the roommate of Paddock

- 22,000 people had been attending the Route 91 country music festival, listening to Jason Aldean perform when the shots rang out just after 10pm on Sunday

- US President Trump has slammed the attack as "pure evil", urging Americans to come together in solidarity

- Flights have been delayed with terrified crowds having run for cover to the McCarran International Airport

- Among the dead include a Las Vegas Metropolitan Police Department officer who was off duty. Two on-duty officers were also injured

Over a period of more than a minute at least four separate periods of sustained gunfire, believed to be from a high-powered assault rifle, were heard as hundreds of deadly rounds were unleashed into the crowd, which included children.

The death toll in the devastating attack, which began to unfold just after 10pm on Sunday night local time, surpasses the Orlando shooting at the Pulse nightclub last year, which saw 49 people killed.

Festival-goers were seen diving for cover as bullets whizzed overhead, with traumatised witnesses claiming they saw victims hit in the head.

The bullets would have created an echo effect around the tall buildings, adding to the terror and panic with people confused as to where the gunfire was coming from.

The shooter was found dead, believed to have killed himself, on the 32nd floor of the Mandalay Bay Resort after SWAT teams stormed the hotel room.

27 New York University students attend a vigil for the victims Credit: AFP or licensors

27 A woman wearing a Route 91 wristband walks near the scene of the attack Credit: Reuters

27 Hundreds of people queue to donate blood following a plea from authorities Credit: Reuters

Although ISIS claimed responsibility for the attack, the FBI said there was no evidence Paddock had any connection with international terror groups.

Police have made progress in their investigations, having located 62-year-old woman, Marilou Danley overseas, who was wanted for questioning in the wake of the attack.

The woman, the roommate of Paddock, holds an Australian passport, having previously been married to an Australian man.

The Australian reported that Danley, who is believed to be a "gambling and casino professional", is possibly of Indonesian descent.

Police said Paddock had been using Marilou's identification, but she was not believed to have been involved.

Two vehicles registered to the Paddock were also found.

Videos taken at the scene appear to capture bursts of gunfire heard in the area, with the 22,000 concert-goers ducking for cover and running for their lives.

Two police officers were among those shot, with at least one killed.

Grieving families have started to name other victims of the brutal atrocity with NEWS 4 revealing music lover Sonny Melton of West Tennessee was among those killed.

27 A man holds a woman injured in the horrific attack Credit: Getty - Contributor

27 People rush to get an injured person help after the worst mass shooting in the US Credit: Getty Images - Getty

27 Broken windows are seen on the 32nd floor of the Mandalay Bay Resort Credit: Getty Images - Getty

27 A woman lies on the ground, covered in blood Credit: Getty Images - Getty

27 Two women hold hands as a group run for their lives Credit: Getty Images - Getty

27 People dive for cover as reports of the horrifying shooting unfolded Credit: Getty - Contributor

27 An officer crouches down for cover, armed with a gun Credit: AP:Associated Press

27 Marilou Danley is believed to have been found by police