(CNN) A 26-year-old man accused of targeting homeless men in a Las Vegas shooting spree has been arrested, the city's police said.

Joshua Castellon was taken into custody last week on a federal weapons charge. He was charged on Monday with two counts of murder and two counts of attempted murder in connection with the shootings , police said.

One of the victims was shot while sleeping under a Las Vegas freeway and another victim was shot and killed while sleeping outside a business, police said.

"These were horrible crimes made worst by the helplessness of the victims," said Cpt. Robert Plummer with the Las Vegas Metropolitan Police Department.

CNN has not been able to determine if Castellon has an attorney.

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