A serial cat mutilator is on the loose in Washington state, killing seven cats so far, authorities said.

The cats were killed and mutilated and purposefully left in parks and front yards for display, animal cruelty investigator Erika Johnson told NBC affiliate K5 News.

“As far as the numbers, it’s probably the worst I’ve seen in my career,” Johnson told K5 News.

The first mutilation was discovered by Johnson in October but there have been more recently. Cats have been found in Tumwater, Lacey and Olympia.

These incidents are happening overnight, mostly from 11 p.m. to 6 a.m., Johnson told K5 News.

The Thurston County Animal Services is working with other police agencies to find the person responsible.

Johnson is urging that owners keep their pets inside the house for the time being and to report suspicious behavior to the proper authorities.