[battle22]

They are mad at him because He didn't talk to him about this, Murder is a serious crime and nothing justifies that, They are mad because, if they found out Keiichi was going to murder Tepei , they would have stoped him no matter what. As for Alibis, As I said It works the same way as Kinzo in Umineko Episode 5, There is a group of people, and during blind spots when nobody can see them, they act as in that person is really there, When the other classmates would notice that they were alone sometimes, they could have thought 'I heard they talking to maebara-san seconds ago, I guess he went somewhere else' .As for Kimiyoshi , they could have told him but either way, Why would someone ask Kimiyoshi such thing, the only person who would do would be Oiishi, and Since Mion moved tepeis body, Sonozaki Family probably knows too so they contacted Kimiyoshi and other people.