CHICAGO (AP) — With no signs of trauma and nothing to raise suspicions, the sudden death of a Chicago man a day after he collected a large pile of 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, theChicago 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, Khan, who owned a number of dry cleaners, stopped in at a 7-Eleven near his home in the West Rogers Park neighborhood on the city’s North Side and bought a ticket for an instant lottery game.

He scratched off the ticket, then jumped up and down and repeatedly shouted, “I hit a million,” Khan recalled days later during a ceremony in which Illinois Lottery officials presented him with an oversized check. He said he was so overjoyed he ran back into the store and tipped the clerk $100.

“Winning the lottery means everything to me,” he said at the June 26 ceremony, 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.

Khan opted to take his winnings in a lump sum of just over $600,000. After taxes, the check, issued July 19 from the state Comptroller’s Office, was about $425,000, said lottery spokesman Mike Lang.

Khan died a day later.

No signs of trauma were found during an external exam and no autopsy was done because, at the time, the Cook County Medical Examiner’s Office didn’t automatically perform them on those 45 and older unless the death was suspicious, Cina said. The cut-off has since been raised to age 50.

A basic toxicology screening for opiates, cocaine and carbon monoxide came back negative, and the death was ruled a result of the narrowing and hardening of coronary arteries.

But a relative came forward and asked authorities to look into the case further, Cina said. He refused to identify the relative.

“She (the morgue worker) then reopened the case and did more expansive toxicology, including all the major drugs of use, all the common prescription drugs and also included I believe strychnine and cyanide in there just in case something came up,” Cina said. “And in fact cyanide came up in this case.”

Chicago Police Department spokeswoman Melissa Stratton confirmed the department was now investigating the death and said detectives were working closely with the Medical Examiner’s Office.