U.S. immigration authorities say a man suspected of killing four people in Nevada over the last few weeks is from El Salvador and entered the United States illegally.

Immigration and Customs Enforcement said Tuesday that 20-year-old Wilbur Martinez-Guzman had no criminal record or history of previous immigration violations.

The agency did not have additional details on his alleged illegal entry to the U.S., including when and where it occurred.

The agency's public affairs staff is furloughed because of the government shutdown

President Donald Trump has seized on the killings to bolster his argument for his proposed border wall with Mexico.

Martinez-Guzman is scheduled to make his first court appearance, Thursday at 1:30 PM in Carson City. Wilbur Martinez-Guzman's arraignment is for six counts including burglary, possession of stolen property and obtaining money by false pretenses. Douglas County District Attorney Mark Jackson says his office will file its criminal complaint this week, charging the suspect with murder.

"The next step in the process is for our prosecuting attorney offices to continue to work collaboratively with the lead detectives in the case," Jackson said. 

Officials will file the charges after they serve an arrest warrant for murder. Investigators say Martinez-Guzman killed Connie Koontz, 56, and Sophia Renken, 74, in Gardnerville. They also say he is responsible for the deaths of Jerry David, 81, and his wife Sherri, 80, in south Reno. 

"Our communities were shaken by these brutal murders and our local law enforcement needs to be commended for their dedication in apprehending Martinez-Guzman," Chris Hicks, Washoe County District Attorney said.

Hicks and Jackson are working together to determine whether or not Martinez-Guzman can be tried for murder in all four cases at the same time. If they do, they will have to decide which venue to hold the trial since the murders happened in two different jurisdictions.

"A conviction for these crimes is our highest priority," Hicks said.

Many northern Nevadans have a lot of unanswered questions about the crimes and the evidence that led authorities to Martinez-Guzman. Some are even fearful that the killer may still be on the loose. The sheriffs from Washoe, Carson City and Douglas County are all confident that they have the right man in custody. Hicks says he knows there are a lot of questions and says the answers will come over time.

"This is to ensure a fair and impartial process," Hicks said. "Our system rests on the defendant's presumption of innocence."

Many others residents are relieved that an arrest has been made, and Hicks is hopeful that it brings some solace to the victims' families.

"Our northern Nevada community needs to embrace the family members of these victims and show them what kind of community we are," Hicks said.

The murder charges against Martinez-Guzman could include enhancements, since a deadly weapon was used in the crimes and because three of the four victims were older than 60. Each enhancement adds one to 20 additional years in prison per charge. First degree murder convictions in Nevada can result in life in prison with or without parole, 50 years in prison with parole after 20 years, or the death penalty. According to the Nevada legislature, the average death penalty trial costs $532,000 more than other murder trials.

Once Martinez-Guzman is charged with murder, he will plead either guilty or not guilty at his arraignment in Justice Court, followed by a preliminary hearing and potential trial in District Court. The court would also appoint psychiatrists and psychologists.

(The Associated Press contributed to this report.)