A glass bottle containing green liquid was thrown at a car as it left the A12 in Woodbridge.
Police are appealing for witnesses to the incident, which happened at 12.05pm on Friday, November 20.
The bottle was thrown at a vehicle driving towards the Wyevale Garden Centre from the roundabout with the A12.
Green liquid ran down the windscreen and a large dent was found in the roof, as well as light yellow/green glass in the rubber seals.
Witnesses or anyone with any information should call Pc David Wright at Suffolk police on 101 quoting reference 16082/15, or Crimestoppers anonymously on 0800 555 111.
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