EndOfTheWorld wrote:But, also, you can't accept MM as the gospel truth.
It's not a question of taking his statement as gospel truth. No witness statement should be taken as such, as witnesses are prone to making mistakes. What you propose as a possibility, however, is that Michael Mageau dreamed up a non-existent detail, namely the t-shirt. This is not the sort of mistake a witness is likely to make. If he had said the attacker wore a green t-shirt, I'd be more than willing to consider it likely enough that the t-shirt was, in fact, red - it was dark, after all. Mistaking another garment (one that would fit your purpose here) for a t-shirt, however, is far less plausible.
We have four separate statements from witnesses who observed Z. Does Michael's description (let's focus solely on body shape/estimated weight here) deviate wildly from the other three? No, it does not. The general consensus among the witnesses is that Z was a fairly heavy-set guy. Whether he was beefy, stocky, overweight, husky - that's up for debate. But
nothing indicates that he was lean or skinny based on what the people who observed him had to say.
You can always come up with ways to cast doubt on said consensus: He wore a disguise which made him look heavier, the witness was in shock, whatever you can think of. What you should ask yourself, however, is whether you're treating the available evidence in an objective manner - or whether you are attempting to make that evidence fit a preconceived notion. You certainly cannot claim that the idea of a skinny Zodiac emerges naturally from the actual descriptions given.