In my opinion, GZ would not have to be a 'criminal mastermind' to say he screamed 'help' - he knew there had been screams that were heard, by all the neighbors emerging. He also knew that TM. the only other person who could say was not moving, no longer being treated by LE or EMT, and had been placed under a tarp.
Knowing that, I believe he would have said he had screamed to explain the noise right away - whether or not he had screamed himself, and not necessarily thinking through the logic - not as a master planner, but to justify the shot he fired - in my opinion.
IMO, only but I read in the emt report (from a link on the documents page here), that attempts to revive TM had been attempted, stopped, and TM was pronounced dead before they treated GZ (which they did, documented his injuries, offered transport to the ER).
While it could be possible that GZ did not know exactly when TM had been pronounced dead, in my opinion he would be fairly certain TM was dead- asking the officer, and seeming surprised isn't evidence of anything - IMO. MOO