Federal authorities are investigating the violent deaths of at least six bottlenose dolphins along the northern Gulf Coast this year, CNN reports ^[2].

The dolphins were shot and stabbed; in one case, jaw of one of the dolphins was cut off, according to CNN.

The Marine Mammal Protection Act makes it a crime to kill dolphins. Scofflaws face up to one year in prison and up to $20,000 in fines.

In an unrelated case, a man was convicted of throwing pipe bombs at dolphins.

“I can’t explain why anyone would shoot a dolphin,” Jeff Radonski, a Florida-based special agent for the National Oceanic and Atmospheric Administration, told CNN.