It might be one thing if the confidential informant in thsi case testified at trial in a burka, or perhaps even (as the government requested) with dark sunglasses.
But he didn't. The CI wanted to partially "disguise" his identity because he was allegedly involved with investigations against the Sinaloa cartel. The trial court let him do so by wearing a fake mustache and a wig. The defendant wanted his conviction reversed on this basis.
There's a Texas state court case that reversed a conviction when a witness was allowed to wear dark sunglasses, a baseball cap pulled down over his forehead, and a jacket with an upturned collar. You can see why. If -- as in that case -- the jury can't view the eyes, mouth, or other facial expressions of a witness, it's going to be much harder for the jurors to judge the witnesses' credibility.
But a fake moustache and a wig don't cover one's face. So Judge Bea holds -- correctly, in my view -- that there's no reversible error here.
I just wanted to add one thing to Judge Bea's opinion. Something that he doesn't mention, but that I view as alternative support for the Ninth Circuit's holding.
Remeber that even normal (i.e., non-CI) witnesses are allowed to grow a mustache. Even normal witnesses are also allowed to wear a wig. Or toupees. Or hair weaves. That's all the CI did here. The only difference is that the CI here did so for reasons apart from trying to look more attractive. But that's a distinction without a difference. If you can wear a mustache or toupee -- and you can -- you can wear 'em regardless of the reason. Whether it's beauty, vanity or "disguise" doesn't matter.
In short: Mustache and hair weaves: Okay. Burkas: Different story.