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 US dollars (£264,550) 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.
"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."
In June, Mr Khan, who owned a number of dry cleaners, visited a 7-Eleven convenience store near his home in the West Rogers Park area on the city's North Side and bought a ticket for an instant lottery game.
Shop assistant Ashur Oshana said Mr Khan told him he had sworn off gambling after returning from the hajj, a Muslim pilgrimage, but bought the ticket and scratched it off in the shop. "Right away he grabbed my hand," Oshana said. "He kissed my hand and kissed my head and gave me 100 dollars. He was really happy."
"Winning the lottery means everything to me," he said at an Illinois Lottery ceremony on June 26, which was also attended by his wife, Shabana Ansari, their daughter, Jasmeen Khan, and several friends. He said he would put some of his winnings into his businesses and donate some to a children's hospital.
The cheque was issued from the state Comptroller's Office on July 19, the day before Mr Khan died, but was cashed on August 15, Mr Lang said. If a lottery winner dies, the money typically goes to his or her estate, he said.
No signs of trauma were found on Mr Khan's body during an external exam and no post-mortem examination was carried out because, at the time, the Cook County Medical Examiner's Office did not generally perform them on people over the age of 45 unless the death was suspicious, Mr Cina said.
Cyanide can get into the body by being inhaled, swallowed or injected. Deborah Blum, an expert on poisons, said: "It has a really strong, bitter taste, so you would know you had swallowed something bad if you had swallowed cyanide. But if you had a high enough dose it wouldn't matter, because... a good lethal dose will take you out in less than five minutes."