DENVER >> The discovery that a Cleveland officer who shot and killed a 12-year-old boy last month had washed out at another police force highlights what some experts call an unnerving truth about policing: Departments don’t always dig deeply enough into recruits’ pasts.

Cleveland police officials didn’t learn until after the Nov. 22 shooting that Officer Timothy Loehmann’s former supervisors at a suburban department noted in his personnel file his “dismal” handgun performance and emotional immaturity. The file shows a deputy chief recommended firing him, but he resigned first.

The Cleveland department has since changed its hiring policy to require reviews of publicly available personnel files.

Authorities say Loehmann believed Tamir Rice, who was playing with a pellet gun, had a real firearm. Loehmann is white and the youngster was black. The shooting added fuel to a nationwide debate about police use of force against blacks in such places as New York City and Ferguson, Missouri.

The Cleveland case “underscores the need for better vetting,” said John DeCarlo, a professor at the John Jay College of Criminal Justice in New York who has studied hiring practices. “We have to be more aware of red flags.”

Police departments typically do a criminal background check and administer a psychological or personality exam, but there are no national standards for screening applicants, he said.

As a result, some departments dig through prior employment files and some don’t, relying instead on interviews with former supervisors or co-workers who are not always forthcoming or honest, and with the candidate’s family and neighbors.

In some cities, such as Denver, retired police and firefighters do those interviews.

In Ohio, personnel files of government employees are public records, so details on Loehmann’s time at the Independence department in 2012 were available to Cleveland officials.

In other states, agencies release records only with an applicant’s permission. But most police departments require applicants to sign a waiver making those files available.

Surveillance video showed Loehmann shot the boy within 2 seconds of pulling up in his patrol car. A grand jury will consider whether to charge the officer.

Loehmann, who joined Cleveland’s force in March, hasn’t commented on the shooting. The police union president has defended the officer’s actions.

Authorities have not made any link between Loehmann’s past job performance and the shooting, but Tamir’s family has filed a lawsuit accusing Cleveland of negligence in hiring him without looking further into his past.

No agency appears to keep statistics on the number of officers who make it onto police departments despite checkered pasts or how many wash out for reasons that should have come to light sooner.

The problem is hard to quantify because an officer’s background often doesn’t come to light unless there is a problem, such as a shooting or misconduct, said Mike Aamodt, a retired professor at Radford University in Virginia who taught courses in employee selection.

Aamodt said the problem may not be widespread, since thousands of good recruits are hired by departments every year. But even a single case is concerning and gives officials reason to review their practices, he said.

Police in Charlotte-Mecklenburg, North Carolina, overhauled their screening process after hiring an officer who later pleaded guilty to sexually assaulting six women during traffic stops. Officials had failed to discover that he had domestic violence allegations and an assault charge against him before hiring him in 2008.

The department now relies on in-house recruiters to conduct background checks, rather than outsourcing the task, spokesman Rob Tufano said.

Michael Vagnini, a former Milwaukee police officer serving time for conducting illegal strip searches on drug suspects, was hired despite allegations he sexually assaulted a female officer while he was a dispatcher for a different department, according to a federal lawsuit. The suit says Milwaukee police accepted Vagnini’s “false and incomplete” version of events rather than checking a disciplinary file that contained witness accounts.

In the late 1980s, Washington police, rushing to hire officers to meet a congressional mandate, brought on scores of recruits without completing thorough background checks. Many had criminal pasts and were later fired or charged with crimes ranging from shoplifting and assault to murder.

Departments should routinely study their own hiring programs and make improvements by scrutinizing their recent hires, Aamodt said.

“You look for mistakes. If you hired someone and the person didn’t work out, what did we miss?” he said.

Improving background checks could be as simple as paying better attention, said Cheryl Dorsey, a retired Los Angeles police sergeant who once conducted interviews with prospective officers.

Dorsey said departments need to be sure they are pulling personnel files when they can, talking to former co-workers and having face-to-face conversations with applicants to get a sense of who they are aside from what’s on paper.

“We’re arming these people. Wouldn’t you want to know everything about this person’s stability, their conduct, their use of common sense?” she said.