Detective Conan: The Time Bombed Skyscraper (1997)

Detective Shinichi Kudo was once a brilliant teenage detective until he was given a poison that reverted him to a 4 year old. He's taken the name Conan Edogawa so no one (except an eccentric inventor) will know the truth. Now he's got to solve a series of bombings before his loved ones become victims. Who is this madman and why is he doing this. Only the young genius can save the day but will even he be up to the task?