In the days prior to July 29, when Mariko Akitaya's lifeless body was discovered floating off the coast of Miura, Kanagawa Prefecture, police say Gregory Gumo, an American resident of Yokohama, purchased a rope and a brown plastic sheet.

On July 27, security camera footage captured images of Gumo and Akitaya traveling in a vehicle in the direction of nearby Atami. Two days later, Akitaya's body was found, wrapped in a brown sheet and attached with rope to a concrete block at the bottom of the shallow bay. She had reportedly been alive when she entered the water, and evidence of drugs used in sleeping pills was detected in her blood. Later on July 29, Gumo was detained at Haneda Airport, where police say he planned to board a plane to the United States. He was charged on Aug. 6 with disposing of a body and the case was sent to prosecutors on Aug. 8.

Kanagawa police believe Gumo, a 41-year-old married father of three, met Akitaya, a 42-year-old single employee in the cosmetics industry, through a dating website. Like most people their age, the victim and her suspected killer left a digital trail across social media and other online sources that may prove useful to police attempting to understand the crime. While Akitaya's online presence was minimal, Gumo — who styled himself as a master event promoter and start-up entrepreneur — left a far bigger footprint that traces the arc of his adult life, from the clubland of his native New York to Japan and Singapore.