Police have arrested innocent people due to faulty fingerprint analysis but have not determined how many cases were affected by such errors, police officials said.

A confidential police report details two cases in which charges were dropped after problems with the fingerprint analysis were discovered, the Los Angeles Times reported late Thursday. Police blame shoddy work and poor oversight for the mistakes.

"This is very, very serious," said Rhonda Sims-Lewis, chief of the Police Department's administrative and technical bureau. "We feel very compelled to take quick action when something like this arises. Guilty people can be set free and innocent people can be jailed."

One fingerprint analyst, who was involved in both the mishandled cases, was fired and three others were suspended last year after internal investigations, Sims-Lewis said. Two supervisors in the department's latent print unit were replaced.

"This is something of extraordinary concern," said Michael Judge, public defender for Los Angeles County. "Juries tend to afford the highest level of confidence to fingerprint evidence. This is the type of thing that easily could lead to innocent people being convicted."

The report details the case of a pregnant hospital technician who was charged with breaking into a store in February 2006 because of an erroneous fingerprint identification. The department said prints in that case were lost and could not be re-examined. The charge was dropped.

In another case, a man was extradited from Alabama to face burglary charges after an analyst matched his prints to those found at the scene. Two reviewers missed the mistake before a third caught it while preparing to testify at the trial.

The department has 78 forensic print specialists who run prints from a crime scene through automated databases to analyze possible matches. Two other analysts check each match for accuracy.

Department officials described a poorly run operation in which records and evidence were lost or misplaced.

"People were reviewing the work of friends and just rubber stamping it without really reviewing it," said Yvette Sanchez-Owens, commanding officer of the department's scientific investigation division.

Critics said the internal report challenges a belief that forensic matches are reliable.

Jack Weiss, chairman of the City Council's public safety committee, said there was "nothing more basic and more bread and butter than fingerprints. You have to be able to take each one of them to the bank." He said he will hold hearings on the issue and call fingerprint lab employees to testify.

"We want to know the extent of it and whether it affects any other cases. We want to know how far back it goes," he said.

Police officials had initially planned to hire an outside expert last year to review the fingerprints unit but could not get the $325,000 to $450,000 to fund the effort.

Sim-Lewis said she believes no innocent people have been convicted of crimes due to fingerprint mistakes by her department, but she acknowledged there was no way to be sure without a full review.

"We still want outside eyes to come in and make sure we're doing things right," she said.

Sandi Gibbons, a spokeswoman for district attorney's office, said her office was investigating how prosecutors could better guard against faulty evidence.