Having your alibi provided only for one out of three murders is not satisfactory. You know that we can't exclude the option of more than one killer working together on the shootings, so taken by itself your tea with Hazama is meaningless.

[ Mikami takes care to make clear that he's got the alibis memorized quite well. He wants everyone to know he isn't messing around - whether or not he makes himself more of a target, justice never bows to injustice. ]