This is what happened to a crocodile at the zoo in Amsterdam. Mating in crocodiles is known to be very violent.
During fornication between two crocodiles, the male dominates the female by locking her head with his mouth to show his superiority. Unfortunately, this time the female crocodile did not survive and eventually died of suffocation.
Note that the crocodile in question, the false gharial Malaysia, is a rare species that has only 2,500 adult specimens in the wild.