The police union warns members that submitting genetic evidence could lead to invasions of privacy. Department officials say the practice is needed to investigate serious use-of-force cases.

Since its arrival as a crime-fighting tool, Los Angeles police officers have aggressively used the power of DNA technology to solve countless cases.

When it comes to handing over their own genetic code, however, they've been told to be a lot more reticent.

For nearly a year, the union representing officers has sparred with the Los Angeles Police Department over the department's refusal to set limits on its practice of collecting DNA samples from officers involved in shootings and other incidents involving serious force. Although rarely done, officers can be required to submit a saliva swab as part of the investigations the department conducts into such incidents.

The Los Angeles Police Protective League, which represents the department's roughly 9,500 rank-and-file officers, warned its members about the issue in an open letter this month, telling them it could lead to invasions of privacy and misuse of the information.

"The privacy issues here are very real," said union President Paul M. Weber in an interview. "Who is to say where the samples will be stored and who will be able to access them? There is nothing more private than DNA."

LAPD officials staunchly defend the practice as a seldom used but important tool. After an officer uses serious force on a suspect, investigators must sometimes test blood, saliva and other genetic material found at the scene in order to determine whose it is and what occurred during the incident, they say.

Attorneys for the league raised concerns about this facet of the internal probes last spring when investigators from the department's Force Investigation Division attempted to gather a saliva sample from an officer who had fired at a suspect. The union did not want to ban the DNA collections, but demanded that the department sign a binding agreement that would have established rules limiting when and how samples can be taken and stored.

LAPD officials refused to sign the document out of concern that doing so could hinder an investigation into an officer's actions. "A good investigation needs to be able to go where it has to go," said Capt. Kris Pitcher, head of the LAPD's Force Investigation Division. "If the investigators look at a scenario and feel they need to gather DNA evidence, then they must be able to do that."

Deputy Chief Mark Perez added that the department does not want to be limited in the way it can use DNA technology. With frequent advances in how genetic analysis can be applied to law enforcement investigations, Perez said the department did not want "to have to go back to the table and renegotiate when something new comes about."

An officer who refuses to give a DNA sample could face discipline for insubordination, Perez said.

Gary Ingemunson, a league attorney, said the union planned to file a protest with the city's Employee Relations Board the next time the department seeks to collect an officer's genetic material. A previous appeal to the board by the union was dismissed on a technicality, union officials said. In the letter to members printed in the union's magazine, police officers were told not to consent to the investigators without first consulting with a union lawyer. "No one can take your DNA without due process," wrote Hank Hernandez, the league's general counsel.

The debate underscores the unusual aggressiveness with which the LAPD investigates incidents in which officers fire their weapons, strike a suspect in the head or resort to other serious force, police experts said. The Force Investigation Division, staffed by about 70 detectives, responds to scores of incidents each year. Teams of investigators typically spend about eight months on an investigation, compiling evidence into 1,500-page reports that are used by the district attorney's office and police officials to determine whether an officer's actions violated any criminal laws or department policies. Law enforcement analysts widely consider the process to be the most thorough in the country.

Pitcher emphasized that it was rare for investigators to take DNA samples from officers, saying he recalled only two cases in the last two years. In one of them, investigators were confronted with a confusing scene in which blood was splattered on a wall and carpet. Both the responding officer and the suspect were bleeding. Blood spatter patterns can reveal much about how a struggle occurred, but investigators first needed to determine whose blood was on the wall by comparing the genetic code contained in the blood.

He added that while the department did not agree to the formal guidelines demanded by the union, the LAPD follows many of them anyway. Namely, the decision to take a DNA sample from an officer must be approved by Pitcher, and an officer is permitted to have an attorney present when the swabbing is done. Officers' DNA samples are destroyed after the investigation, Perez said.

Regardless, union officials expressed concern that the department's restraint today could give way to more widespread testing in the future. Weber, the league president, and Hernandez also said that despite assurances from the department, they do not trust the LAPD to safeguard officers' DNA from mistakenly being uploaded to state and national databases kept for criminal investigation purposes.

"In such cases, there will be a greater chance of officers being erroneously accused of a crime," Hernandez wrote.

"Your league is not a big advocate of allowing officers to give up anything to anyone without . . . a legal requirement."

Indeed, this is not the first time union and department officials have clashed over officers' personal information. The union has waged a bitter battle over an anti-corruption policy passed last year that requires officers in specialized assignments who frequently handle cash and other contraband to disclose personal financial information. After losing several court decisions on the matter, the union is currently awaiting the outcome of an appeal to the U.S. 9th Circuit Court of Appeals.

League officials and law enforcement analysts said they know of no other police department in the country that collects DNA from officers as part of their internal investigations into shootings and other uses of force. Police in Britain are more aggressive, storing the genetic profiles of nearly 100,000 officers and support staff who work at crime scenes in a database to prevent them from falling under suspicion during investigations, according to Britain's Home Office, the country's equivalent of the U.S. Justice Department.