A memorial was held Sunday for a Westchester County police officer who was fatally shot by four officers when he tried to stop a mugging in White Plains.

Hundreds of people mourned Officer Christopher Ridley on the one-year anniversary of his death. Ridley was killed by the officers who, while responding to the mugging, mistook him for a criminal because he was off duty and dressed in plain clothes.

County Executive Andrew Spano dedicated 85 Court Street Plaza in White Plains in Ridley's honor. In Mount Vernon, a massive crowd surrounded the steps of police headquarters for a street dedication.

After Ridley's death, a panel made up of citizens and law enforcement officials was formed to come up with ideas for safeguards to prevent a similar friendly fire incident from happening again.

The group came up with more than 60 recommendations and at least 45 of the suggestions have been implemented, including new training techniques for Westchester County police officers, who are now required to attend an annual tactical training day.