Previous posts pretty much cover it, but don't bother shooting at the big monster, just run around and doubleback a lot. When you get a bit ahead of it go to one of the 4 psi judges on the beds and hold action until the pins retract and they fall from the chairs. Don't kill them, although the real Dredd would do this in a Mega City minute, killing them fails the level.
Once all 4 (or is it 3?) Psi judges are free you should be rewarded with the pisspoor end sequence.