'Serial killer' targeting sleeping homeless in Las Vegas

A serial killer is targeting sleeping homeless people in Las Vegas just months after the city suffered unspeakable tragedy in America's worst mass shooting.

The gunman is said to be about 1.8m tall and preys on homeless men, according to the New York Post, stalking them while they sleep then shooting them.

So far, the shooter has killed two people and left two more with injuries.

James Lewis, 64, was found dead on February 2. He was sleeping under the Vegas bridge about four kilometres from where another homeless man was found dead on January 29.

Surveillance video shows the killer executing Lewis as he slept.

Mr Lewis' daughter, Oneida Lewis Baker, told ABC News the person responsible "doesn't deserve to have freedom" and hopes they are caught.

"I am praying that he doesn't kill anybody else or even injure anybody else," she said.

"I don't want anyone to go through what I am going through."

Las Vegas Metropolitan Police Department said the shooter first opened fire on a man outside a convenience store just after midnight on January 29. The target - and the only victim not homeless - suffered non-life-threatening wounds.

Three hours later the shooter fired at a group of homeless men sleeping outside a shopping centre leaving Brian Clegg, 51, dead.

At 7am, just four hours later, another homeless man was shot in the face near the city's centre, but he survived. He couldn't provide any details about his attacker.

Mr Lewis was killed days later. Police said the same gun was used in all four attacks.

Las Vegas has one of the largest homeless populations in the US, with an estimated 10,500 living on the streets. Police have increased patrols but still don't know who's responsible.

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Police captain Robert Plummer described the shootings as "cowardly".

However, the FBI does not consider whoever's responsible for the killings to be a serial killer. The bureau defines a serial killer as someone who had a month between murders, meaning the shooter's actions would technically be defined as a "spree killing".

But Capt Plummer disagrees with the FBI.

"After killing two people and shooting two others, if he isn't (a serial killer), he's on his way to being one," he said.

The body of Michael Hadley, 25, was also found on February 3 in Cold Creek, in the desert northwest of the city, according to Fox News. Police said it appeared Mr Hadley was a homicide victim, but would not connect his death with the others in the city.

Investigators added Mr Hadley was known to frequent Las Vegas, and it's not known how long his body was in the desert before it was found.