A serial killer thought to be responsible for the fatal shooting of six men and the wounding of one woman in California since April 2021 seems to be “on a mission”, police said.

Ballistics tests and some video evidence have linked the crimes in the cities of Stockton and Oakland, located about 70 miles apart in the US state, police said.

Stockton police chief Stanley McFadden said: “We don’t know what the motive is. What we do believe is that it’s mission-oriented. This person’s on a mission.”

The first fatal shooting took place in Oakland in April 2021. The woman was wounded in Stockton days later.

More than a year passed before five killings took place in Stockton between July 8 and September 27, all within a radius of a few square miles.

Although police would not say whether all seven shootings are linked to the same gun, Mr McFadden alluded to a single pistol during a news conference.

The police chief said he has “absolutely no answer as to why that pistol went dormant for over 400 days”, between the April 2021 shootings and the first case this summer.

Authorities said five men in Stockton were ambushed and shot dead, alone in the dark.

On Monday, police said the two additional cases last year have been tied to those killings.

A person of interest is being sought in connection with the bloodshed – they appear on video at several of the crime scenes – but no evidence directly links them to the shootings, McFadden said.

He said some of the victims were homeless and some were not.

There is a 125,000 dollar (£109,000) reward for information leading to an arrest. Police are fielding hundreds of tips every day, as well as submitting additional evidence in case other crimes in the state can be connected to the spate of shootings.

The first killing targeted Juan Vasquez Serrano, 39, in Oakland at around 4.15am on April 10 2021.

He was shot multiple times, according to the Alameda County coroner’s bureau. It was not immediately clear if he was alone when he was killed.

In the non-fatal attack, the 46-year-old victim told investigators that she was inside her tent on April 16 2021 at about 3.20am when she heard someone walking around outside.

“When she came out of her tent, she encountered someone holding a gun,” Mr McFadden said.

The suspect fired multiple shots, wounding the woman, but she tried to defend herself by advancing toward her attacker, the chief said. The shooter then lowered the gun.

“She said there were no words mentioned at all,” Mr McFadden said.

The woman described the attacker as wearing a dark hooded sweatshirt with the hood pulled up, dark trousers and an all-black face mask, of the type commonly used during the Covid-19 pandemic.

In the fatal Stockton cases, none of the men were robbed or beaten before the killings, and none appeared to have known one another, Stockton police officer Joseph Silva said. The shootings do not appear to be related to gangs or drugs.

The San Joaquin County Office of the Medical Examiner identified the Stockton victims as Paul Yaw, 35, who was found dead on July 8; Salvador Debudey Jr, 43, who died on August 11; Jonathan Hernandez Rodriguez, 21, who was shot on August 30; Juan Cruz, 52, who died on September 21; and Lawrence Lopez Sr, 54, who was killed on September 27.

Stockton is a city with a population of 320,000, about 50 miles south of the state capital, Sacramento.