CHICAGO (AP) – With no signs of trauma and nothing to raise suspicions, the sudden death of a Chicago man just as he was about to collect nearly $425,000 in lottery winnings was initially ruled a result of natural causes.

Nearly 6 months later, authorities have a mystery on their hands after medical examiners, responding to a relative’s pleas, did an expanded screening and determined that Urooj Khan, 46, died shortly after ingesting a lethal dose of cyanide. The finding has triggered a homicide investigation, the Chicago Police Department said Monday.

“It’s pretty unusual,” said Cook County Medical Examiner Stephen Cina, commenting on the rarity of cyanide poisonings. “I’ve had one, maybe two cases out of 4,500 autopsies I’ve done.”