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Over the course of one week, two homeless men were shot dead in Las Vegas while sleeping, according to police officials in the city.

Another homeless man was stabbed to death, but it is unclear if the three slayings are related, officials said

"Over the last week, we’ve had three homicides involving homeless," Las Vegas Metropolitan Police Department Capt. Robert Plummer said at news conference on Friday. "One stabbing and two shootings. ... It’s important that the community understands that the Las Vegas Metropolitan Police Department cares about the homeless. We ask that the community care as well."

The most recent killing took place early Friday when 64-year-old James Edgar Lewis was shot while sleeping under an overpass in downtown Vegas.

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Las Vegas police released graphic video of the shooting, captured by surveillance cameras, in an effort to identify the suspect.

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In the video, a vehicle is seen passing Lewis, who appears to be asleep on the sidewalk. The vehicle then makes a U-turn and a man exits and approaches on foot. The suspect walks up to Lewis and extends his arm before two flashes can be seen from the end of what appears to be a gun.

The suspect can then be seen running from the scene. Throughout the video, Lewis never moves; his body was found hours later.

"There's no fight. There's no argument. It's basically an execution," Lt. Dan McGrath of the police department said during the news conference.

A suspect's vehicle passes by a sleeping homeless man in downtown Las Vegas before an adult male emerges from the car and shoots the homeless man. Las Vegas Metropolitan Police

The Clark County Coroner's Office confirmed to NBC News that Lewis died of a gunshot wound to the head.

The make and model of the suspect's vehicle has yet to be determined.

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Last Monday, Jan. 29, another homeless man was shot while sleeping behind a shopping area, according to The Las Vegas Review-Journal. And just a day earlier, a homeless man was found outside a gas station suffering from a stab wound and later died, authorities said.

Officials said they are using forensic testing to determine if the killings are related.

McGrath said the police department was working with the FBI to enhance the video of the Lewis' shooting to try to identify the suspect.