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RENO, Nev. — A 19-year-old Salvadoran man suspected of being in the country illegally was charged Monday with killing four people in Nevada, including a couple who employed him as a landscaper at their Reno home where he fatally shot them with a gun he stole from them earlier, authorities said.

Wilber Ernesto Martinez-Guzman told investigators he used a .22-caliber revolver stolen from the property of 81-year-old Gerald David and 80-year-old Sharon David less than two weeks before he killed them on Jan. 16.

"The lady was coming out. I got scared and shot at her," Martinez-Guzman is quoted telling a Washoe County detective in an affidavit filed in Reno on Monday. It alleged that he first broke into "outbuildings" or a trailer on the sprawling David property on Jan. 3 and Jan. 4 and made off with a cache of rifles and the handgun.

Wilbur Martinez-Guzman. Carson City Sheriff's Office via AP

Martinez-Guzman had worked for a landscaping company at the Davids' property for four months, ending last July. It was not immediately clear if the job linked him to two women he is accused of killing in nearby Gardnerville.

The affidavit was used to obtain an arrest warrant for Martinez-Guzman, who was arrested Jan. 19 in Carson City and is jailed there on charges that he possessed weapons and other items stolen from the Davids and sold jewelry belonging to Gerald David and another victim.

Martinez-Guzman admitted also killing Gerald David, and the affidavit alleges that his DNA was found on the .22-caliber gun also used to kill Connie Koontz and Sophia Renken in their homes. Koontz was found dead Jan. 10. Renken's body was found Jan. 13.

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The Davids were prominent Reno Rodeo Association members, and Martinez-Guzman is accused of possessing several Western-style belt buckles bearing their names stolen from their home.

Someone using an Apple account belonging to Martinez-Guzman's mother tried to activate an Apple watch stolen from Koontz, the affidavit said.

The mother, identified in the affidavit as Sonia Guzman, hasn't been charged with a crime. She was questioned by immigration authorities following her son's arrest and was given a hearing date, Carson City Sheriff Ken Furlong said.

Guzman was the registered owner of a 2006 BMW 325i that Martinez-Guzman was driving when he was arrested, and in which authorities say they found the murder weapon.

The .22-caliber revolver was recovered from the car, and the affidavit said a .22-caliber bullet with DNA matching Martinez-Guzman was found on the kitchen floor at the David home.

Douglas County District Attorney Mark Jackson told reporters Monday that investigators in Douglas and Washoe counties had "a high level of confidence" that Martinez-Guzman acted alone in the killings.

Washoe County District Attorney Chris Hicks refused to comment on his immigration status.

President Donald Trump tweeted a week ago that the four killings in Nevada showed the need for his proposed U.S.-Mexico border wall, which was at the center of the federal government shutdown.

"What someone's status is in this country has nothing to do with how we are proceeding in this case," Hicks told reporters Monday. "We are looking to hold an alleged murderer accountable for the murders he committed. That's all."

Hicks said it would be more than a month before prosecutors decide whether to pursue the death penalty against Martinez-Guzman.

The 30-day clock on that decision deadline doesn't begin until he's formally arraigned in district court on the murder charges along with five burglary charges added in the new criminal complaint.

Hicks said they intend to extradite Martinez-Guzman to Washoe County to face those charges as soon as possible and that he will be held without bail in the county jail in Reno but that his initial arraignment in Reno Justice Court has not yet been scheduled.

He's currently being held in the Carson City jail on the theft and burglary charges on $500,000 bail. His appointed public defense attorney there, Karin Kreizenbeck, has declined comment.

Furlong said earlier that Martinez-Guzman's only known contact with authorities was a speeding ticket last February.

Each of the district attorneys told reporters during a news conference in Reno on Monday they would co-prosecute the case personally as their "highest priority."