Denjiro Maru, an antique collector, asks Kogoro to investigate his wife's affair. Denjiro is later found pinned to a wall with a katana. The crime scene has been shredded with a sword and clues point to different people who had scheduled meetings with the collector.
Using his gadgets to use Kogoro, Conan reveals that the killer is Yuji Suwa.
While Suwa was fiddling with the answering machine to prove he wasn't the killer, with the last of his strength, Denjiro wrote Suwa's name on the drawers for a dying message to prove he was the killer. When Suwa noticed this, he shuffled the drawers then added a few more markings so it couldn't be recognized, and marked the rest of the room so it wouldn't stand out, to erased a dying message from the police's eyes.
Suwa then charged at Kogoro with a sword to kill him, but stopped just when the sword was about to hit deep into Kogoro's head. Suwa claims Kogoro must be very brave to just stay still in the face of death. After Suwa was arrested however, Kogoro finally wakes up and notices a tiny drip of blood on his head and freaks out.
Suwa's family had an antique sword that was passed down from generation to generation, but Denjiro sold it. Suwa couldn't control his anger that Denjiro sold his family heirloom, so he gave him the kill.
In the manga, Denjiro is shouting a couple times for someone to greet the visitor at the door before realizing he gave the staff time off and sent them out due to having a detective over. Kogoro asks if his wife was told to leave as well with Denjiro mentioning that she left at noon for a Koto lesson, though he's disbelieving due to the photo. Afterwards, he leaves to greet his visitor while mentally cursing Ineko. In the anime, Denjiro simply calls for someone to answer the door once before realizing that his staff is out and simply goes to greet the visitor.