Oakland police officials believe the driving factor in a roughly 50 percent drop in gun-related killings and injuries in the past seven years has been their partnering with community organizations in an effort called Ceasefire that focuses on people considered most at risk of becoming a shooter or victim.

The Oakland Ceasefire program, which was started in early 2013 and mirrors similar initiatives across the country, provides certain individuals the opportunity to receive help and mentoring in what are known as “call-ins,” a bid to guide them away from future harm. They are also warned that continued violence or retaliation after a shooting could lead to legal consequences and put their lives at further risk.

In 2011, Oakland saw 93 gun homicides and 617 nonfatal victims of gun assaults, according to a report on the city’s Ceasefire progress released Tuesday by criminologists and researchers from Northeastern University, Northwestern University and Rutgers University. In 2017, there were 63 homicides and 277 nonfatal gun assaults — reflecting a 48 percent drop in total cases from 2011.

“Instead of doing what we normally would have done for a very long time in the city of Oakland, attempting to go out and put as many people in jail as possible, we came up with an idea that we were going to have a strategic approach,” said Oakland police Capt. Ersie Joyner, who directs Ceasefire for the department.

Joyner said police identified three chief goals for the program: reducing shootings and homicides, reducing recidivism, and repairing and building law enforcement’s “damaged relationship” with the community.

Vaughn Crandall, co-director of California Partnership for Safe Communities, explained that officials develop program rosters that include people who are at risk of re-offending, victims of nonfatal shootings and those who are likely to be drawn into the “cycle of retaliation” following a shooting. They pair these individuals with “life coaches,” mentors primarily hired from Oakland organizations such as Community & Youth Outreach, Youth Alive and the Mentoring Center.

“We engage them and inform them of their risk of the likely legal consequences if they were to use a gun to retaliate, of the special services and opportunities and supports that are available to them now and in an ongoing way,” Crandall said. “The primary focus is to build trust, help them stay safe and out of prison.”

When intervention doesn’t work with clients, said Oakland Mayor Libby Schaaf, a Ceasefire supporter, law enforcement is the “last resort, but it is a threat that gets used when necessary.” Joyner joined Schaaf and Acting Deputy Chief LeRonne Armstrong in acknowledging the historic distrust of law enforcement agencies, especially among communities of color.

As part of their effort to improve public trust, Armstrong said every city police officer and professional staff member has undergone an initial eight-hour training session on the history of the community’s distrust of the Oakland Police Department.

“We recognize that No. 1, we were going into neighborhoods that trust us the least but needed us the most,” Joyner said. “We set out five years ago with this paradigm shift in regards to our service delivery ... and we had to recalibrate our officers into using procedural justice.”

Joyner said clients of the program have taught officials how to better understand the fears of those participating in the program.

“They told us about how they feel vulnerable driving to certain locations for a call-in because they have to pass through rival gang territory,” Joyner said. “Saying that right now, I feel like an idiot that I didn’t recognize that right away, but that was something that we did for them.”

The university researchers — who isolated census blocks in Oakland that included gangs or groups brought in for Ceasefire intervention — estimated that the program reduced city gun homicides by 31.5 percent through 2017. The report analyzed a group of 12 other “comparison” cities in California and only two — San Francisco and Stockton — showed significant reductions during the same period.

The study also said Ceasefire was associated with a 27 percent reduction in shootings by “treated” Oakland gangs and groups relative to those not targeted. Specific individuals “treated” by officials were either part of a group that was a focus of Ceasefire interventions, attended call-ins, received communication from law enforcement or were referred to social services from Ceasefire officials.

Crandall said most gun violence in big cities is driven by a small group of people who are “highly involved” in the justice system, and Oakland is no different.

“What you see in that analysis,” he said, “is that the majority of homicides in Oakland are connected to ongoing conflicts between identified street groups.”

Lauren Hernández is a San Francisco Chronicle staff writer. Email: lauren.hernandez@sfchronicle.com Twitter: @LaurenPorFavor