Pig: Officer! Help! Help! There's been a murder of crows! Cop: Ha ha. Very amusing. A group of crows is called a "murder." Now run along and prank someone else. Pig: Some crimes are so hard to report.
Actually a bit of better word choice would clear things up easily. “Crows have been killed.” “I’ve found crows with knives sticking out of them.” Even “Someone murdered these crows.”.Pig, the way you said it was the only way that would make things difficult. And yes, saying it that way sounds very much like a prank.