Police are looking for the man who caused thousands of pounds worth of damage to two police cars.
CCTV from Abbotts Langley police station shows someone smashing in the rear side windows of both vehicles and setting them alight on Monday at 3am.
The suspect is described as a tall, thin, white man who wore a long blue puffa jacket, black trousers and black footwear with a white buckle. He was carrying a green jerry can in an Asda bag.
Det Con Gordon King said: “This will not only cost the tax payer, but could have led to a much more serious incident if the fire spread or the petrol tanks exploded.”
Call the non-emergency number 101 or Crimestoppers on 0800 555 111 with information.