A memorial to a policeman stabbed through the heart by a teenage hitchhiker in 1977 has been unveiled.
PC Norman Garnham was killed by Colin Simpson moments after offering him a lift in Richmond, North Yorkshire.
Simpson, who had been trying to hitch a ride after attacking his sisters, was given a life sentence for murder.
Sgt Amy Hunter helped establish the memorial after learning she shared the same collar number as PC Garnham.
Unveiling the plaque she said she wanted people to remember the 25-year-old's "name, his service and the sacrifice he made".
PC Garnham was driving home from work when he stopped to help 18-year-old Simpson.
Upon realising he was a police officer, Simpson stabbed the constable in the chest.
He fled the scene but was arrested an hour later as he tried to hitch a lift on the A1, near Scotch Corner.
Then chief constable Robert Boyes described PC Garnham as "a police officer of the very best quality".
The plaque has been placed on the courtyard wall of The Green Howards' Museum in Richmond.
Assistant Chief Constable of North Yorkshire Police, Phil Cain, said: "Norman was murdered following an initial act of kindness that sadly led to his untimely death.
"We must never forget the sacrifice that he made and that such tragic events can happen anywhere, and sadly still do."