[How did Hijikata find out that the experiment to stop Saya's hibernation cycle failed? Well, he tried to call her several times after he expected the test to have concluded, and no one picked up. Consequently he eventually went to the Research Centre, and the researchers there told him what happened (not that they shared all the grim details).
Rosen never told Hijikata his apartment number, but a policeman has his ways. So he ends up in front of his door, knocking. Part of him hopes that Rosen isn't actually at home. He, himself, wouldn't be able to stand being alone after losing a partner so cherished and beloved. But if he is here, then Hijikata wants to keep his promise to Saya and be there for him.
Backdated to June 25th
Rosen never told Hijikata his apartment number, but a policeman has his ways. So he ends up in front of his door, knocking. Part of him hopes that Rosen isn't actually at home. He, himself, wouldn't be able to stand being alone after losing a partner so cherished and beloved. But if he is here, then Hijikata wants to keep his promise to Saya and be there for him.
He knocks again.]
Rosen? Are you there? It's Hijikata.
[His voice probably gave that away.]