Police are investigating the deaths of five cats which were apparently struck with an object deliberately.
A sixth cat which suffered similar injuries is being treated in Brentwood, Essex Police said.
The force said that a concerned vet contacted police after members of the public brought in cats they believed had died after being hit by a car. Upon further inspection, it appeared that the fatal injuries could have been caused by the cats being struck with an object, police said.
She said the cats are thought to have been injured in the Pilgrims Hatch and Kelvedon Hatch areas of Brentwood between Friday and Tuesday.
Police are appealing for anyone who witnessed suspicious behaviour or believes their car may have struck a cat to contact them.
They also want to speak to the people who brought the cats to the vet surgery to establish where they were found, to establish if they were in the same place.
Anyone with information is asked to call Brentwood local policing team on 101 or Crimestoppers on 0800 555 111.