Chris Darden thinks once a double murderer, always a double murderer ... and that's why he thinks the Florida Attorney General may have a point in trying to block O.J. Simpson from moving to the Sunshine State.

We got the famous O.J. prosecutor at LAX Friday and -- even though O.J. was acquitted -- Darden still calls him a double murderer. He worries for unlucky parents who might end up living next door to Simpson.

Darden has no faith O.J. has been rehabilitated in the last 9 years behind bars.

And then there's the possibility of another Bronco chase ...