A suspected serial killer in the California city of Stockton was arrested Saturday and police say they believe he was "out hunting" when he was nabbed.

"We are sure we stopped another killing," Chief Stanley McFadden, of the Stockton Police Department, said at a news conference Saturday.

Wesley Brownlee, 43, was arrested in connection with six unprovoked murders of men ages 21 to 54 over the last few months. He was booked on a homicide charge Saturday.

Police said that surveillance teams followed Brownlee while he was driving, and stopped in area of Village Green Drive and Winslow Avenue around 2 a.m. Saturday morning.

"Our surveillance team followed this person while he was driving. We watched his patterns and determined early this morning; he was on a mission to kill. He was out hunting," McFadden said.

McFadden added, "As officers made contact with him, he was wearing dark clothing and a mask around his neck. He was also armed with a firearm when he was taken into custody."

Brown will be arraigned Tuesday and more charges are likely, police said.

The San Joaquin County's Office of the Medical Examiner identified the victims. Paul Yaw, 35, was killed on July 8; Salvador Debudey Jr., 43, died on Aug. 11; Jonathan Hernandez Rodriguez, 21, was killed on Aug. 30; Juan Cruz, 52, was the Sept. 21 victim; and Lawrence Lopez Sr., 54, was slain on Sept. 27.

The men were alone at the time when they were fatally shot, officials said. All of the killings took place at night or in the early morning hours, police said.

Another shooting, of a 46-year-old Black woman at Park Street and Union Street in Stockton at 3:20 a.m. on April 16, 2021, was also linked to the investigation, police said earlier this month. The woman survived her injuries in that shooting, they said.

Police said that a motive is not known for the killings but it is believed to have been intentional.

ABC News' Mark Osborne and Emily Shapiro contributed to this report.