A California man who was arrested in connection with a series of killings in Stockton was charged with three counts of murder and accused of using a so-called ghost gun in the slayings.

Wesley Brownlee, 43, was charged for the shooting deaths of Jonathan Rodriguez Hernandez, 21, Juan Carlos Carranza-Cruz, 52, and Lawrence Lopez, 54, the San Joaquin County District Attorney’s Office said.

He also was charged with one count of a felon in possession of a firearm and one count of possession of ammunition.

Wesley Brownlee was dressed in black, wore a mask around his neck, had a handgun and “was out hunting” for another possible victim when he was arrested while driving around the Central Valley city, where five of the shootings took place, Police Chief Stanley McFadden said at a Saturday news conference.

Police believe the same person was responsible for killing a man 70 miles (113 kilometers) away in Oakland in April 2021 and wounding a homeless woman in Stockton a week later.

Investigators have said ballistics tests and video evidence linked the crimes. A police photo showed the black-and-gray weapon allegedly carried by the suspect. It appeared to be a semi-automatic handgun containing some nonmetallic materials.

Juan Vasquez Serrano, 39, was killed in Oakland on April 10, 2021, and Natasha LaTour, 46, was shot in Stockton on April 16 of that year but survived. The five men killed in Stockton this year were Paul Yaw, 35, who died July 8; Salvador Debudey Jr., 43, who died Aug. 11; Jonathan Hernandez Rodriguez, 21, who died Aug. 30; Juan Cruz, 52, who died Sept. 21; and Lawrence Lopez Sr., 54, who died Sept. 27.

Police said Brownlee has a criminal history and is believed to have also lived in several cities near Stockton, but they did not give further details.

McFadden added that Brownlee was detained after engaging in what appeared to be threatening behavior, including going to parks and dark places, stopping and looking around before driving on.

Investigators were still processing evidence and trying to identify a motive for the attacks, Officer Joseph Silva, a police spokesperson, said Sunday. Police said some victims were homeless, but not all. None were beaten or robbed, and the woman who survived said her attacker didn’t say anything.

The police chief thanked various local, state and federal agencies that took part in the investigation, including the FBI, U.S. Marshals and U.S. Drug Enforcement Administration.