(CNN) The video is chilling. James Edgar Lewis is sleeping under a Las Vegas freeway when a dark-colored SUV passes by. Seconds later, a man wearing a dark top emerges from the vehicle and shoots Lewis twice in the head before fleeing.

There is no struggle, no fight. Lewis never even appears to wake up.

"It's basically an execution," said Lt. Dan McGrath of Las Vegas Metropolitan Police.

Lewis was the latest of four homeless men who have been shot in Vegas in recent days. Two have died.

Three men were shot January 29 within about a seven-hour span. Lewis' death came four days later on February 2, said Las Vegas Metropolitan Police Capt. Robert Plummer said

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