Sean disappeared from Seattle, Washington on July 5, 2008. His parents, Carl Hillman and Mayumi Ogawa, married in 2000. Sean attented bilingual English and Japanese preschools, visited Japan and made many Japanese-American friends during his early childhood. After his parents divorced, they had a joint custody agreement where both of them were supposed to have equal access to their son.

Carl went on vacation with Sean, then dropped him off at Ogawa's residence on July 5. They were supposed to visit Ogawa's native Japan for a few weeks, visit her family, and return in time for Sean to start classes in a Japanese/English immersion program at the John Stanford International School. Ogawa promised to return her son on time and posted an $8,000 bond to guarantee this. She and Sean never returned to the United States, however; instead, they settled in Tokyo, and Ogawa's lawyer warned Carl not to contact them or he would face charges of stalking. Carl has since been awarded sole custody of Sean and Ogawa was charged with felony first-degree custodial interference. Photographs and vital statistics for Ogawa are unavailable.

Carl has attempted through legal and diplomatic means to have Sean returned to his care, but the Japanese government usually doesn't recognize American custodial decisions. He has had more success than most left-behind parents, however: when Ogawa asked a Japanese family court to name her Sean's sole custodial parent, the judge refused and acknowledged Carl's custodial rights. The court ruled that jurisdiction for determining Sean's custody lay in the United States. Carl has also been permitted to visit his son in Japan a couple of times, but Sean has yet to be returned to the United States. He is a United States citizen and was born and raised in that country until his abduction.

Although Sean's whereabouts are known, he is listed as a missing child because his custodial father doesn't have him in his care.