The culprit is Meisuke Oozumi. He stabbed the victim out of jealously that he was too close to his girlfriend. The trick he used to see through the peep hole was to put tape on it to flatten the surface of the frosted glass to see. He also practiced himself in his house to stab in the dark at his drama club's room and even drew sketches of the setting in cafe Poirot in his notebook. To avoid getting blood on himself, he wrapped his arm around toilet paper and put the toilet paper's roll aound the knife to limitate the quantity of blood to splatter and directed the knife towards Heiji and Conan so that was why they got blood on themselves. Before the lights opened, he flushed the toilet paper, put the roll back and retrieved the tape on the peephole. Amuro remarked that the toilet paper roll was a bit odd and seemed to have been forced. The truth is that Tengo is actually the half-sibling of Oozumi's girlfriend Yui. The victim, Tengo, even recorded a birthday message for Oozumi telling the truth about his relationship with Yui. This was kept a secret because it would cause a career ending disaster for Yui's father, who is a dietman, for having fathered a lovechild. Heiji found the truth because of the hint Momiji ordered Iori to reveal and she also heard a scratch of the tape on the peep hole when Anzai was stabbed. After Yui revealed him the truth, Oozumi bursts into tears and receives a phone call from Anzai that told him that it hurted when he stabbed him.
It's revealed that 'Shinichi Wada' is actually Muga Iori, the butler of Momiji Ooka's family. He went to Poirot on Momiji's orders to observe Heiji. He mentions to Momiji that while Heiji is interested in another girl, it shouldn't prove a problem for Momiji. He also promised that he will do his best to support her.
