The culprit is Shigehide Kariya. Eisuke Kariya is actually hiding in the Kariya's house's attic, and he was being protected by Shigehide.
Ran thinks that Tsugutaka might have known about his wife having an affair, since he always got mad, whenever there was a door bell prank or phone call prank.
People
Tomoko Kariya
Victim (bludgeoned)
39 years old
Kogoro Mouri's client
Married to Tsugutaka
Daisaku Kariya
68 years old
Kariya household head
Shigehide Kariya
37 years old
Kariya's second son
Author
Tsugutaka Kariya
42 years old
Kariya's eldest son
Tomoko's husband
Artist
Eisuke Kariya
Kariya's third son
Missing
Motoka Aida
Deceased (bludgeoned)
Eisuke's fiancé
Major events
Ran get suspicious of Conan's identity again...Shinichi gives Ran his personal cellphone number.