1. Go to the last level (Aye mak sicur)
2. Search a narrow and dark corridor (there
are lots of these so you'll need to search a while)
3. At the end of this corridor you can jump down. Don't
do it, but
4. Stand on the ledge before the pit and push the "action" key.
5. You should hear something opening in front of you.
6. Now run forward and jump into the pit.
7. You should now arrive at a dark hall with a 'credits' terminal.
Read it and make sure you're at "Total Carnage" level.