Wilbur Ernesti Martinez-Guzman, 19, was arrested Saturday afternoon by deputies from the Carson County Sheriff's Office, Washoe County Sheriff Darin Balaam told a news conference Sunday.
"We feel confident we have the evidence to link him to all four homicides," Balaam said.
Investigators said the killings started on or around Jan. 10 in Gardnerville, a town south of Carson City. Connie Koontz, 56, was found shot and killed in her home. On Jan. 13, 74-year-old Sophia Renken was found dead in her home approximately a mile away from Koontz.
The FBI joined the investigation after the bodies of married couple Gerald David, 81, and Sharon David, 80, were found in their home on the southern edge of Reno Wednesday. Balaam told The Associated Press on Friday that all four killings were similar in the use of a firearm and the removal of objects from the victims' homes.
The sheriff urged residents to turn on outside lights, secure their homes and refuse to open the door for anyone they didn't know.
On Sunday, Douglas County Sheriff Dan Coverley told the Reno and Carson City communities: "We feel strongly that we have the man responsible for this and that you can continue to go about your daily activities and live normally."
Carson City Sheriff Ken Furlong told reporters a tip led investigators to surveil Martinez-Guzman, who had lived in the Carson City area for approximately one year. Furlong added that immigration officials had said that Martinez-Guzman "was likely in the United States illegally and was detainable."
Martinez-Guzman was being held in the Carson City Jail on Sunday and was charged with burglary, possession of stolen property and obtaining money under false pretenses. Furlong added that an immigration hold had been placed on the suspect, who was not known to his office.
Washoe County District Attorney Chris Hicks said authorities would seek arrest warrants against Martinez-Guzman for the murders "in the coming days."
The Associated Press contributed to this report.