LAS VEGAS (AP) — A man suspected of being in the U.S. illegally shot and killed four people in Nevada over the past two weeks, including an elderly Reno couple, authorities said, and the slayings added fuel to the immigration debate.

Wilbur Ernesto Martinez-Guzman, 19, from El Salvador, has been jailed in Carson City since Saturday on possession of stolen property, burglary and immigration charges. Authorities said they expect to file murder charges against him in Reno in the shooting deaths of a Washoe County couple and in Douglas County in the slayings of two women in Gardnerville.

Carson City Sheriff Ken Furlong said federal immigration authorities told his office that Martinez-Guzman was in the country illegally. Immigration and Customs Enforcement did not have details on his entry into the U.S.

The investigation is ongoing, the sheriff said, and it was too early to comment on a possible motive.

Investigators who had been tracking Martinez-Guzman considered him “an imminent threat” when they arrested him Saturday afternoon in the parking lot of a shopping mall.

“We couldn’t account for him Friday night, and we couldn’t predict what he would do Saturday night,” Furlong told The Associated Press. “It was too great a risk to the public not to make the arrest.”

Detectives had watched Martinez-Guzman go to a car wash and trash bins, raising concern that he might try to dispose of evidence connected to the slayings. He did not have a weapon when he was handcuffed, the sheriff said.