RENO, Nev. >> A man suspected by authorities of being in the U.S. illegally shot and killed four people in Nevada over the past few weeks, officials said, adding fuel to the immigration debate.

While it wasn’t immediately clear today where 20-year-old Wilbur Martinez-Guzman was from or how he came to the U.S., President Donald Trump has seized on the killings as evidence of the need for his proposed U.S.-Mexico border wall.

“Four people in Nevada viciously robbed and killed by an illegal immigrant who should not have been in our Country,” Trump said in a tweet Monday. “We need a powerful Wall!”

Martinez-Guzman has been jailed in Carson City, in northern Nevada near the California border, since Saturday on possession of stolen property, burglary and immigration charges.

Authorities have said they expect to file murder charges against him in the shooting deaths of an elderly Reno couple and two women in the nearby town of Gardnerville.

Carson City Sheriff Ken Furlong said that federal immigration authorities told his office that Martinez-Guzman was in the country illegally.

Authorities have said Connie Koontz, 56, was found dead Jan. 10 in her home. Three days later, 74-year-old Sophia Renken was found dead in her home about a mile (1.6 kilometers) from where Koontz lived.

On Jan. 16, the bodies of 81-year-old Gerald David, and his 80-year-old wife, Sharon, were found in their home on the southern edge of Reno.

Furlong said the investigation is ongoing and that it was too early to comment on a possible motive.

He said Martinez-Guzman did not yet have an attorney who could comment on his behalf.