Crazy Kick-Ass Crocodiles

"So, I was on the web, today, a moment ago, like I am now, and I came by this image of the Ninja Turtles chasing a Crocodile humanoid, or Mutant Alligator,
and it got me thinking:

Now that they made a new Ninja Turtle movie, in 3D CGI;~ What is the official storyline for the ninja turtles?

1.) Are they sewer mutants?
2.) Or are they successful scientific experiments?
3.) Or had they always been successful scientific experiments, with very little knowledge of their origins.

I thought this was relevant to the existence of this new character.
I think for me they will always be sewer mutants... but I am subject to change in the event of a compelling explanation of the plot.

"Crazy -
Kick - Ass
Croco-
Diles.
Crazy -
Kick - Ass
Croco-
Diles.
CRAZY-
KICK - ASS
CRoc -
ODilEs.
Somethings Going on here!"

Fun fact: the alligator man would be much younger than the Ninja Turtles, and thus subject to his juvenile psychological traits, making him naïve and malleable.
Friend or Foe?