(CNN) -- No cyanide remained in the exhumed body of Illinois lottery winner Urooj Khan, preventing investigators from determining how the toxin entered his body, the Cook County medical examiner said Friday.
Still, Dr. Stephen Cina maintained his determination from January: that blood samples taken after Khan's death in July show the 46-year-old died of cyanide poisoning, and that the manner of death was homicide.
Officials in January exhumed the body of Khan -- who died the day after the Illinois lottery issued him a check for about $425,000 for winning a scratch-off game -- hoping to determine how cyanide entered his system.
"Cyanide has a short half-life, and it may be lost over the postmortem interval unless the tissues are adequately preserved," Cina said Friday. "In this case, due to advanced putrefaction of the tissue, no cyanide was detected" after the exhumation.
Investigators initially ruled Khan's manner of death natural. But after being prompted by a relative, technicians retested Khan's blood, leading to Cina's cause of death determination in January, more than a week before the body was exhumed.
Cina also said Friday that coronary artery disease was a contributing cause to Khan's death, because the autopsy showed one of his major coronary arteries was 75% blocked.
"Since cyanide affects oxygen utilization in the tissues, it follows logically that a natural disease process that already limits blood flow to the heart could render an individual particularly susceptible to death due to this toxin," he said.
Before the exhumation, Cina told reporters that cyanide can evaporate from a body after death, and that it was possible it would not still be present.
The autopsy results have been turned over to Chicago police, who have been investigating the case as a murder.
CNN's Shawn Nottingham contributed to this report.