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 six 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.