Police have said at least five people fired weapons in a weekend shooting in Sacramento, California, that killed six people and injured a dozen others and prompted calls for lawmakers to address the scourge of gun violence in the US.

Officials said on Wednesday that while the motive was still unknown, investigators think “ gang violence is at the center of this tragedy” and that “gangs and gang violence are inseparable from the events that drove these shootings”.

Police have made three arrests since the violence that unfolded around 2am on Sunday morning. Smiley Martin, who was also injured in the shooting, has been charged with possession of a firearm by a prohibited person and possession of a machine gun, while officials have charged his brother Dandrae Martin with assault and illegal firearm possession offenses.

Daviyonne Dawson faces charges of being a prohibited person in possession of a firearm. The 31-year-old was reportedly seen carrying a weapon in the area, but police say he was not charged for the shooting and officials don’t believe the gun was used in the incident. Dawson has posted a $500,000 bail and is no longer in jail.

Law enforcement sources told the LA Times on Wednesday that the incident looked to be a shootout between “rivals” and that bystanders were caught in the crossfire of more than 100 shots. The shooting took place as bars in the areas closed and patrons headed to the streets. Police have confirmed they are investigating whether the incident could be connected to a street fight that broke out before gunfire erupted.

No one has been charged with homicide in connection with the shooting as detectives continue with a complex investigation that includes hundreds of pieces of physical evidence, video footage, photos and dozens of witnesses.

Authorities think the Martins had stolen guns. Investigators are trying to determine if a stolen handgun, which was converted to a weapon capable of automatic gunfire, found at the crime scene was connected to the shooting.

Mass gun violence has shaken the region in recent weeks, raising questions about what can be done to stop the proliferation of illegal firearms in California. Less than six weeks ago, a man shot himself in a Sacramento suburb after killing his three daughters, ages nine, 10 and 13, with a ghost gun, a firearm without a serial number that is typically purchased online and assembled at home.

California already has some of the nation’s strictest firearms rules, but has yet to find a way to deter those willing to skirt the laws with stolen or homemade and increasingly prevalent ghost guns.

Gavin Newsom, California’s governor, has proposed a law that would allow citizens to sue anyone who distributes illegal assault weapons, parts that can be used to build weapons, guns without serial numbers, or .50 caliber rifles. Under the measure, which is patterned after a controversial Texas bill aimed at abortions, those who sue would be awarded at least $10,000 in civil damages for each weapon, plus attorneys fees.

“California leads the nation in enacting robust gun laws … and we’re still seeing this unprecedented level of gun violence,” said Robert Hertzberg, the Democratic state senator who is carrying the bill, to a senate committee. “There’s still much to be done, and we need to be creative.”

But experts and analysts have raised questions about the effectiveness of the proposed law, warning that it would encourage civil actions to punish crimes and that is so broadly written it could ensnare, for instance, “a taxi driver that takes a person to a gun shop”.

The bill is patterned after a similar Texas law allowing citizens to go after those who provide or assist in providing abortions. And even if it becomes law, it will automatically be invalidated if the Texas law is eventually ruled unconstitutional.

Meanwhile, it emerged that one of the men arrested in connection with the shooting was recently released from a California prison, a few years into a 10-year sentence.

Smiley Martin, 27, was released from prison on probation in February after serving his term for punching a girlfriend, dragging her from her home by her hair and whipping her with a belt, prosecutors said. An earlier parole bid was rejected after prosecutors said he posed “a significant, unreasonable risk of safety to the community”.

Dandrae Martin, 26, who was held without bail, was freed from an Arizona prison in 2020 after serving just over 18 months for violating probation in separate cases involving a felony conviction for aggravated assault in 2016 and a conviction on a marijuana charge in 2018.

Small memorials with candles, balloons and flowers remained near the crime scene on the outskirts of the city’s main entertainment district honoring the six people killed. Officials identified the dead as Johntaya Alexander, 21; Melinda Davis, 57; Yamile Martinez-Andrade, 21; Sergio Harris, 38; Joshua Hoye-Lucchesi, 32; and De’vazia Turner, 29.

Alexander, an aspiring social worker, was just shy of her 22nd birthday. “She was a strong-willed person in the prime of her life and she was killed in a senseless shooting,” her father, John Alexander, told the Sacramento Bee. “She was down there with her sister, trying to have a good time.”

Melinda Davis was a “very sassy lady”, a friend told the newspaper, and lived on the streets of Sacramento near the site of the shooting.

Described by relatives as the life of the party, Harris was a frequent presence at the London nightclub, near the shooting scene. His mother called him a “very vivacious young man” who was always smiling.

Hoye-Lucchesi was born and raised in Sacramento and his survivors include his mother, his girlfriend and six young children, KCRA 3 reported.

A friend told KXTV-TV that Martinez-Andrade, who was killed in front of her best friend, “brought light to the room”.

Turner, who grew up playing football in Sacramento, had four young children and worked out with his father five days a week.