Police are hoping to track down the retired colleagues of a fallen officer ahead of a memorial dedicated to him.
Frank Mason was off-duty when he was shot in the back while bravely trying to stop an armed robbery in Hemel Hempstead on April 14, 1988.
Friday will mark 25 years since his life was cut short. His former colleagues and local people are invited to pay their respects to him by attending a memorial service at Bank Court on the day from 12.30pm.
Each year Herts Constabulary also presents an award in his memory to an outstanding officer.
If you worked with PC Mason please contact Kevin Deudon on 01442 271010.