A Haunted Mansion Murder Case

Resolution
Hide= Evidence
 * -|Show=
 * There is a working secret entrance that allows entry or exit onto the grounds without being seen by anyone else.
 * The house still has running water.
 * A window had been left open, with no signs of wind or rain wear.
 * The house shows no overt signs of life, but the kids smell something cooking.

Conclusion
 * The house is not abandoned, but rather hides the dead mansion owner's wife and son, Akio.
 * Akio killed his father with a single blow to the head. Unlike many other suspects, Akio had actually intended to turn himself in as soon as he could, but his mother decided to protect him. Her "protection", however, meant locking Akio in the basement until the statute of limitations for the murder expired and he couldn't be prosecuted. He tried to convince his mother otherwise but she was so desperate to not lose her son and apparently only relative left that she wouldn't listen to his pleas. Eventually, as she loses it and attempts to kill the children for snooping in the now abandoned home, Akio manages to stop his mother and insists that he should atone for his crime; with Conan's help, this time he is successful, and both mother and son turn themselves in together.

Motive
 * Akio killed his father in the heat of an argument over how he had flunked an important university exam, having impulsively grabbed a bronze candle holder and hit his father in the head with it. He did NOT intend to murder him, however, and was emotionally broken when he realised what he had done.

Manga to anime changes

 * The manga version of the story marks the debut of Mitsuhiko Tsuburaya, Ayumi Yoshida and Genta Kojima. In the anime, they appear in the first episode.

Trivia

 * Mitsuhiko says that they are going to investigate Shinichi's house which he says "is the last house on the left" a clear allusion to the 1972 film of the same name.