What a fucking bum. This guy loses credibility 2 minutes into the whole thing.
The set of circumstances are as follows:
1.) Windows gets the keys from Garry
2.) Windows finds Bennings being assimilated, drops the keys
3.) The men burn Bennings and look for Blair
4.) Blair goes apeshit and destroys the radio
5.) Men lock up Blair and discuss the blood-serum test
6.)Garry gives Doc the keys
7.) Fuchs and Doc discover the blood has been tampered with
8.)The men argue over who could have opened it. Garry and Doc are the prime suspects as they both had access to the keys. Windows begins to freak out because he dropped the keys earlier and is afraid they're going to call attention to that fact, and they've already created a Garry/Windows dynamic which plays out a few minutes later when Garry threatens to kill Windows.
Bennings was wasted before they even thought of the blood-serum test, and the blood isn't tampered with until AFTER they've discussed the possibility that they can "detect" who has been infected. The keys are reintroduced after Windows drops them but before they find the storage blood destroyed.
The more interesting question is when was Blair assimilated? Before or after the radio room rampage?