When you pay close attention to the song When the Darkness comes and pay attention to the footprints you'll notice one subtle hint with when it goes to Aka Sensei. The footprints seem to symbolize a part of the person and when they change for Aka it shows a tiny bomb on the foot print then again it could just be an apple but it looks like a bomb. then not to mention aka would have been at the idol bombing and would have had time to set up it. this also includes that she was the teacher for Meteor who gave the alibi according to Detective Detective in Im Sorry. She would have had the time to do the tampering before the date since more then likely Kanesaki was still helping her out. bringing that into account she could have had the means to tamper with the Star Blush Girl's bags even before the bombing. which would allow her to plant the blame on them not to mention she would have had access to the backstage area since she was the teacher of the idol group of Meteor. She would have had the time and the means to do it but the only thing missing is a motive which can be elaborated on as more episodes are released.