Kaho Mizunuma
did not commit a suicide or was murdered, but is actually hiding at
Maki Ohara's house for her own safety.
Four months ago, Kaho witnessed a murder committed by Jun Naruse, who threatened to kill her should she reveal his crime. Kaho tried to contact the police, but was dismissed due them believing the case to be an accident. Driven to despair, Kaho attempted to commit suicide at the bridge after riding in Maki's taxi to the location.
Although Maki resented her at first for being weak-willed and wanting to die, unlike her daughter who fought her illness to her very last breath, and thought of killing Kaho herself, she had a change of heart and decided to protect Kaho. Being an ex-swimmer, Maki disguised herself as Kaho and pretended to commit suicide by jumping off the bridge during the time Tetsuya Ushio would be in the area. Conan realized that Kaho is still alive due to the following reasons: the shoelaces were tied differently, Maki was buying contact lens despite having no vision problem along with two lunch boxes, and the woman who jumped off the bridge in the video was wearing a jewelry despite Kaho herself being allergic to metal accessories; with the last one used as an evidence that Naruse was pretending to be her boyfriend as he didn't know about her condition. Additionally, although Naruse cut and dyed his hair to differentiated himself from the wanted poster, the tattoos on both of his arm is the decisive evidence that he is the prime suspect from the murder case four months ago.
Full of gratitude for Maki's help, Kaho decides to not run away anymore and testifies against Naruse.
Following Kaho's testimony, the college girl murder case is reopened by the police and Naruse is convicted for his crime.
Aftermath
At the end, Kogoro, Ran, and Conan are in the Detective Agency and receive cookies made by Ohara and Mizunuma together, who became best friends.