ANTIOCH — A city facing a critical shortage of police saw its resources stretched even thinner during a violent 8-hour stretch ending Wednesday, as two people were killed in separate incidents and a shootout between two groups injured another person.

Hours before the violent night began, investigators learned that an 83-year-old man who had been brutally beaten during a robbery outside a hardware store almost four weeks earlier had died of his injuries.

The combination stoked residents’ fears about continuing violence and prompted city leaders to pledge to fully staff the department as soon as possible — and urge voters to approve a tax increase that would fund even more officers.

Patrick Chang, 83, of Antioch, died Tuesday morning at John Muir Medical Center, weeks after a May 18 assault during a robbery in the parking lot of Orchard Supply Hardware on Lone Tree Way. A 15-year-old boy was arrested May 23 on suspicion of the robbery and assault.

An autopsy performed Wednesday found that Chang had died from traumatic brain and spinal injuries. Prosecutors said they were considering whether to seek a homicide charge against the juvenile suspect.

Around 5:45 p.m., police were called two a two-story home in the 4400 block of Horseshoe Circle, where they found the body of Ronald Henry Rush, 70. Police said Rush had suffered head trauma, and they were treating the case as a homicide.

Less than 30 minutes before the discovery of Rush’s body, police responded to a shootout in the 2200 block of L Street and chased down a wounded man who ran from them after two groups of people opened fire on each other.

Police found him hiding in a backyard on Manzanita Way, suffering from at least two gunshot wounds. The man, who was uncooperative with investigators, did not sustain life-threatening injuries, police said.

About seven hours later, police said Roberto Lopez, 21, also of Antioch, was shot in the 1900 block of D Street downtown at 12:26 a.m. Wednesday while riding his scooter from a friend’s house. He later died at a hospital. Police do not have a motive, but described Lopez as a suspected gang member.

The three deaths doubled Antioch’s homicide total for 2013, taking the number from three to six in one day. There were 10 homicides in 2012 and five in 2011.

The overnight spate of violence was particularly taxing on the city’s short-staffed police department, which has the same number of officers it did in 1993, when the city’s population was almost half of the 104,000 living there now.

There are 87 sworn officers in the department, down from 126 in 2008, and several units — traffic, narcotics, special enforcement, school resource — have been cut, said Tom Fuhrmann, head of the Antioch police officers’ union.

The city council has authorized the hiring of additional officers to a maximum of 102, but the hiring process is moving at a snail’s pace, said Fuhrmann.

“We’re keeping our head above water as best we can,” said Fuhrmann. “It’s a grind. Not just a grind on you physically but mentally with your personal and professional life.”

Police Chief Allan Cantando said about 20 patrol officers and investigators were able to work on each homicide thoroughly but that other calls for service were impacted, including the L Street shootout.

“That’s why I’ve been advocating for an increase in police staffing and a dedicated funding source,” Cantando said. “If we were able to have a larger presence in the community and special response teams, there’s a very good chance that they may have been in custody for something else, say a traffic violation, and not out committing a homicide.”

Said Brittney Gougeon, founder of Facebook-based civic group Take Back Antioch: “I think basically there’s just a high level of frustration and mental and emotional exhaustion from having to read and see it, either in the media or from neighbors, or hearing gunshots in neighborhoods.”

“I have to remind people that crime is cyclical and sometimes the timing is just really bad.”

Gougeon said Antioch is seeing a similar pattern to what is happening in San Jose, where there is a direct correlation between decreased police presence and an increase in crime. Of all large Bay Area cities, Antioch had the steepest increase in violent crime, with a jump of 30.6 percent between 2012 and 2011, FBI statistics show.

“Other communities that have full staffs, their crime rates tend to be lower,” Cantando said. “It’s something we saw coming when (2010’s half-cent sales tax) Measure P didn’t pass. At what point is our community going to say, ‘We’re not going to take this anymore’?”

City leaders are considering placing a pair of tax initiatives on the November ballot. The decision to put the companion half-cent sales tax and landlord fee measures before voters will be made June 25.

“We’re not wavering on our resolve,” Mayor Wade Harper said. “We’re going to continue to do everything we can to make Antioch a place where it is known that if you do something wrong, you will get caught.”

Contact Rick Hurd at 925-945-4789, Paul Burgarino at 925-779-7164 and David DeBolt at 925-779-7166.