A group of 11 Northern Virginia police departments said Tuesday it has launched a Critical Incident Response Team to handle the investigations of police shootings, in-custody deaths and officer suicides in one another’s departments, allowing a group of detectives unrelated to the involved department to take an independent look at each case.

But three of the largest law enforcement departments in Northern Virginia — the Fairfax County police, the Loudoun County Sheriff’s Office and the Alexandria police — have not joined the response team. Fairfax said it had confidence in its detectives’ ability to be fair and transparent, and Loudoun and Alexandria said they work with the Virginia State Police when a deputy or officer is involved in a serious use-of-force incident. Fairfax and Loudoun declined to join, while Alexandria’s city council is still considering joining.

When a police officer shoots someone, resulting in injury or death, that officer’s own department typically handles both the criminal investigation, to see whether the officer should be arrested, and the internal investigation, to see whether the officer broke any department rules. But many experts and activists feel that a police department’s investigating its own officer is potentially unfair: The investigator may know the officer involved and be biased for or against the officer, or may want to keep the department’s reputation clean.

Last month, the President’s Commission on Law Enforcement and the Administration of Justice recommended every state require its police departments to have an independent agency investigate all fatal shootings and other serious use-of-force incidents by officers as a way of restoring and supporting public faith in policing.

The new response team will provide “a high degree of impartiality and separation over these large cases,” said Manassas City Police Chief Douglas Keen, because its detectives will “not be reviewing their own agency or peers. This will promote public confidence within each of our communities.”

Herndon Police Chief Maggie DeBoard, who also is the head of the Virginia Association of Chiefs of Police, said, “The outcries for police reform have been ringing really loudly across the nation over the last 10 months. In Virginia, we have eagerly embraced it.”

DeBoard noted that the Northern Virginia Police Chiefs and Sheriffs Committee began working on the idea in December 2019, at the suggestion of Keen and then-Arlington County Police Chief M. Jay Farr. “One of the most difficult things for a police officer to do is to investigate one of their own,” DeBoard said. She said the experience can be traumatizing for the investigators as well as the officer.

The agencies that have committed to the response team are Arlington County; Fairfax City; Falls Church; Herndon; Leesburg; Manassas; Manassas Park; Prince William County; Purcellville; Vienna, and the Metropolitan Washington Airports Authority police. Each police chief will have the option of calling in the response team, which will use experienced detectives from other jurisdictions to handle the investigation. Those detectives will then file a report with the commonwealth’s attorney in the jurisdiction where the event occurred, and that prosecutor will decide whether charges should be filed. Internal investigations still will be handled by the original department.

“The important part of this is I don’t have control of that investigation,” DeBoard said. “I have control over the information I release to the community.” The original department will still handle public news releases, she said.

Though some have argued prosecutors should recuse themselves from handling police cases in their own jurisdictions, because they regularly work with the officers there, no such agreement was reached with the commonwealth’s attorneys in Northern Virginia. Kean said the local prosecutors were “engaged in the process” of creating the response team but will retain their own jurisdiction.

The commonwealth’s attorneys in Fairfax and Alexandria declined to comment Tuesday. Arlington Commonwealth’s Attorney Parisa Dehghani-Tafti said in an email, “I think as prosecutors we should be willing to be transparent, just as we demand of the police.” Prosecutors are publicly elected every four years, unlike police chiefs, and have long argued they are elected to make decisions on whether to charge officers.

In Washington, the Metropolitan Police Department investigates its own officers’ shootings, as does the Prince George’s County department. In Montgomery and Howard counties, the police investigate their own shootings, but prosecutors in a neighboring county oversee the investigations and review the cases for possible charges.

Fairfax, with more than 1,450 sworn officers, is twice the size of any other department in Northern Virginia. Fairfax Police Chief Edwin C. Roessler Jr. said in a statement that he supported the goals of the response team and that Fairfax would provide technical assistance as requested. But he did not say why Fairfax was not a full participant.

The last controversial fatal shooting by a Fairfax police officer was investigated by Fairfax homicide detectives beginning in 2013 and resulted in an involuntary manslaughter conviction of the officer. Adam Torres was convicted of killing unarmed Springfield resident John Geer. After the Geer case, a civilian review panel and independent auditor post were created, and Roessler has begun promptly releasing information about shootings, including the names of officers involved.

Fairfax homicide detectives also joined the investigation of the 2017 U.S. Park Police killing of unarmed motorist Bijan Ghaisar in Fairfax, leading to manslaughter charges against the officers. Roessler released video of the shooting over federal objections. In cases where officers from one jurisdiction are involved in a shooting in another jurisdiction, decisions about whether to launch the response team will be made at the time, Keen said.

In Alexandria, the city “committed in 2018 to refer 100 percent of applicable cases to the Virginia State Police,” city spokesman Craig Fifer said, to include not only shootings but any accusation of a criminal offense by an officer. He said the city council was still considering participating in the response team as well as in a civilian review board for the police.

A spokesman for Loudoun County Sheriff Mike Chapman said the sheriff uses three options for a deputy-involved shooting: have Loudoun’s detectives investigate it themselves; conduct a joint investigation with the Virginia State Police; or have the state police perform the entire investigation. Spokesman Kraig Troxell said Chapman decides which option to use on the basis of the circumstances and complexity of a case. Loudoun has about 560 sworn deputies.

But many of the departments that joined the response team Tuesday are smaller, with fewer resources. Purcellville has about 15 sworn officers, Manassas Park and Falls Church have about 30 each. “Especially for small departments,” said Falls Church Police Chief Mary Gavin, “it’s hard to sustain the manpower” needed for an extensive investigation. “And because we’re so small, we don’t have all the expertise we may need in these cases. The CIRT is an exceptional resource for us.”

Gavin noted state police “don’t have the resources to do all the officer-involved shootings throughout the commonwealth. This was the way for Northern Virginia to ensure they would get a thorough, complete and neutral investigation.”

Gavin said she hoped Fairfax, Loudoun and Alexandria “will join as [the response team] gains experience. I respect the fact they don’t want to right now, but let’s see how things play out and the group gets more experience.”

Dan Morse contributed to this report.

This report has been updated to reflect that Alexandria has not decided whether to join the response team.