LOS ANGELES—A judge Dec. 12 rejected a bid by more than two dozen Southern California cities for an injunction blocking Los Angeles County’s use of a “zero-bail” system, but the cities were given time to amend their complaint.

The legal challenge to the zero-bail system was filed in September, just days before it took effect on Oct. 1. The coalition of cities argued that eliminating cash bail and allowing many arrestees to be either booked or cited and quickly released from custody presented a danger to public safety.

Their request for a preliminary injunction halting the program and returning the county to a cash-bail system was denied Monday by Orange County Superior Court Judge William Claster, who also ruled that the municipalities had failed to assert a viable cause of action.

However, Judge Claster agreed to give the cities until the end of January to shore up their arguments.

“We appreciate the court’s decision to allow us to present additional evidence of the harmful impacts of No-Cash Bail,” the coalition of cities said in a statement responding to the ruling. “This sweeping program was implemented too quickly without adequate research, or enough input from the communities it affects. We believe we can do better.

“As our coalition prepares additional data for the court, city leaders will continue to prioritize public safety in advocating for smart reforms to the justice system. We look forward to continuing our work with the courts and our local communities to find safe and positive outcomes for all residents of L.A. County.”

Backers of the zero-bail system, formally known in the county as Pre-Arraignment Release Protocols, or PARPs, say it eliminates a long-standing discriminatory detention policy that favored the rich who were able to post bail, while leaving lower-income people to languish in jail, unable to raise bail money for even the most minor of offenses.

The program provides “a pretrial release system in which the decision to release arrestees charged with non-violent, non-serious criminal offenses from jail prior to conviction is no longer determined by a person’s access to money,” Los Angeles Superior Court Executive Officer/Clerk of Court David Slayton said in a statement Monday. “Instead, their release status is determined by risk to public or victim safety and their likelihood of returning to court. This is consistent with the constitutional purpose of bail, which is to ensure an arrestee appears for all court appearances and to reduce the risk to public and victim safety.”

After the first month of the PARP implementation, county officials released data showing that the system was working “exactly the way it was intended” and had not decreased public safety.

The report compiled by the court found that less than 3 percent of people who were booked on suspicion of a crime were subsequently re-arrested and booked again during the first three weeks of the PARP system.

The zero-bail system largely eliminates the existing cash bail system for all but the most serious of crimes. Most people arrested on suspicion on non-violent or non-serious offenses are either cited and released in the field or booked and released at a police or sheriff’s station with orders to appear in court on a specific date for arraignment once they are actually charged with a crime.

Arrestees who are believed to present a heightened threat to the public or be a flight risk are referred to a magistrate judge, who reviews the case and determines whether the person should be held in custody pending arraignment or released under non-financial restrictions such as electronic monitoring.

Once a person is charged and appears in court for arraignment, a judge can change or revoke the defendant’s release conditions.

Some law enforcement officials, including Los Angeles County Sheriff Robert Luna, expressed concern about the system before it took effect, saying it would reduce public confidence in the justice system by quickly releasing people arrested for a variety of offenses.

But Superior Court officials said arrest data from the program’s first three weeks belied those concerns.

According to the report, 40 percent of bookings during that time were for more serious offenses that were ineligible for zero-bail consideration. A total of 1,213 cases were referred to a magistrate judge for further review, and of those, 64 percent of the arrestees were ordered to remain in custody pending arraignment.

The report found that 85 percent of people released under the zero-bail system were considered low-risk offenders, while 71 percent of the people held in custody pending arraignment were considered medium- to high-risk.

The report found that only 2.5 percent of people who were booked during the first three weeks of the program were subsequently re-arrested for another offense and re-booked. Of that 2.5 percent, nearly half of the re-arrestees had been arrested for a serious or violent crime and were free only because they posted cash bail. Only two people who were released after a review by a magistrate judge were re-booked during the first three weeks of the program, according to the report.