S01E673: Detectives' Nocturne (Deduction)

Conan stops feigning his sleep and tells his kidnapper she is actually Serina Urakawa and that Kei Katshitsuka was the dead man at the agency; his deduction stemmed from a phone call to Shouno's relatives to find out the identity of his girlfriend. Conan explains that Katshitsuka and the man in the apartment were two of the three robbers. Urakawa learned from Shouno that Katshitsuka was one of the robbers. When visiting his apartment, she meets the second robber whom she killed in self-defense. After learning that Katshitsuka plans on meeting with Kogoro to find out which locker the money was hidden in, she attempts to interrogate him and fashions his murder as a suicide by drugging him, placing the gun in his hands, and pulling the trigger with a string. As for the third robber, Urakawa plans on visiting the three female contacts found on Katshitsuka's phone to determine which one is the culprit.