Yamamoto was last seen in Bothell, Washington on September 29, 2009. He lived in the Park Lane Townhouses. He has never been heard from again. He wasn't missing until the middle of that month; as he lived alone and kept to himself, no one realized he was gone. It wasn't until November that the apartment manager notified his family in California that he was missing, and filed a report with the police. Yamamoto normally only contacted his family at Christmastime.

On October 10, Yamamoto's car was found at O.O. Denny Park in Kirkland, Washington. It was towed several days later. The police didn't realize at the time that Yamamoto was missing, so they didn't search the car until November 20. They found no indications of foul play. There was an empty bag for an inflatable kayak, suggesting Yamamoto went kayaking out on Lake Washington. This theory hasn't been proven and his kayak and paddle have not been recovered. The kayak is red and gray.

Yamamoto usually paid his rent three months in advance, but the day before his disappearance he gave the apartment manager a check for only one months' rent, saying that was all he had. It's unclear whether this is related to his disappearance or whether he was in financial trouble. He was raised in Tokyo, Japan and graduated from the Brooks Institute of Photography in California. His sister describes him as a skilled photographer and guitar player. His case remains unsolved.