To become an alibi in the future for the other person, that's correct! However, that makes this much more complicated, and assumes we have two such devious people amongst us! Someone devious would wait until later, when they have a better read on everyone, rather than jumping at murder the first chance they get! It's possible, certainly, yes!

But to open ourselves to that possibility from the start opens the playing field rather than narrowing it down. I am not arguing it is impossible, I am arguing it is unlikely and we have more to gain by checking the simplest solution first! Ichigo-kun, don't be so fussy!