In episode 2, Yamane Yukihiro tells Nishinosono and Professor Saikawa that the director isn't there, he's off picking up Dr. Magata's younger sister, Miki.
Nishinosono: Where did the director go?
Yamane: He went to get Dr. Magata's younger sister.
However, we later learn that Miki was actually Dr. Magata all along. This means that the director was aware this is the day he would die all along. How though, was this plan between Dr. Magata and the director communicated? I understand that all communications were recorded. They also said multiple times that no one had gone in to Dr. Magata's room for 15 years, except they did open the door anytime they had to put a large package in.
What was the method they used to communicate this plan?