As colleagues cheered him on, a Mexican policeman pumped 10 gunshots into a protected species of crocodile crawling out of a lagoon, sparking outrage on social media, officials said.
The officer now faces charges over the killing in the town of Ahome in the northwestern state of Sinaloa.
The animal was of the species Crocodylus acutus, or American crocodile, which has protected status in Mexico, the environmental agency PROFEPA said Monday.
The agency learned of the killing through a video posted on social media last weekend, the agency said.
The creature was killed for no reason, it said.
However, Sergio Liera, head of Civil Protection in Ahome, said his department ordered the animal killed because it posed a threat to local people, the agency statement said.
In the video, a policeman is seen shooting the crocodile more than 10 times. Other officers and people looking on cheered as he fired his gun.