( CNN ) -- One day , Urooj Khan jumped for joy after scoring a $ 1 million winner on an Illinois lottery scratch ticket . The next month , he was dead . Investigators initially ruled Khan 's manner of death natural . But after being prompted by a relative , the medical examiner 's office in Cook County , Illinois , revisited the case and eventually determined there was a lethal amount of cyanide in Khan 's system . `` That ... led us to issue an amended death certificate that ( established ) cyanide toxicity as the cause of death , and the manner of death as homicide , '' Chief Medical Examiner Dr. Steve Cina said Monday . Why did Khan , an Indian immigrant who was described as a well-liked , hardworking and successful businessman , die ? And who is responsible ? Finding that out is now up to the Chicago police . No arrests have been made . `` We are investigating it as a murder , and we 're working closely with the medical examiner 's office , '' Chicago police spokeswoman Melissa Stratton said Monday . On June 26 , Khan was all smiles at a 7-Eleven in the Rogers Park section of Chicago . Surrounded by his wife , daughter and friends , he held an oversized $ 1 million check and recalled his joy upon playing the `` $ 3 million Cash Jackpot ! '' game , where tickets sell for $ 30 apiece . `` I scratched the ticket , then I kept saying , ' I hit a million ! ' over and over again , '' the 46-year-old Khan said , according to a press release from the Illinois Lottery . `` I jumped two feet in the air , then ran back into the store and tipped the clerk $ 100 . '' The plan , he explained , was to use the money for his mortgage , paying off bills , a donation to St. Jude Children 's Research Hospital and investing more in his dry cleaning businesses . Related : The problems with winning the lottery . `` Winning the lottery means everything to me , '' Khan said . He would have to wait a few weeks to collect his actual winnings , which amounted after taxes to about $ 425,000 . According to CNN affiliate WGN , that check was issued July 19 , but Khan never got to spend it . The next night , Khan came home , ate dinner and went to bed , according to an internal police department document obtained by the Chicago Tribune . His family later heard him screaming and took him to a local hospital , where he was later pronounced dead , the paper reported , citing the document . That 's where the Cook County medical examiner 's office came in , investigating Khan 's death because it was `` sudden and unexpected , '' Cina said . At the time , there were no allegations of foul play or evidence of trauma . So , following the office 's policy , Khan 's body underwent what Cina described as an `` external examination ( and ) basic toxicology testing , '' neither of which turned up anything abnormal . So the medical examiner ruled that Khan had died of arterial sclerotic cardiovascular disease -- which encompasses incidents like heart attacks , strokes and aortic ruptures -- and that his manner of death was natural , according to Cina . A few days later , a family member approached the doctor who had examined the body `` and said they felt uncomfortable that it was being ruled a natural and they suggested that we look into it further , '' the chief medical examiner said . `` So we did that , '' he added . `` Forensics is not a static field . If new evidence comes to light , we 'll revisit cases . '' That meant more in-depth toxicology tests . In early September , new screening results came back indicating cyanide in Khan 's blood . With that , the official manner of death was changed from natural to pending , Cina said , and Chicago police got involved . In late November , a more detailed blood analysis came back showing `` a lethal level of cyanide , '' and Khan 's death became a murder case . Chicago police have n't offered details , including a possible motive , about what they call an `` ongoing investigation . '' Talking briefly with CNN affiliate WBBM and the Tribune , Khan 's widow described her husband as kind and exemplary . Jimmy Goreel , who runs the 7-Eleven where the winning lottery ticket was sold , offered similarly glowing comments about Khan . `` I would never think that anybody ... would hurt him , '' Goreel told WGN . `` ( He was a ) nice person , very hopeful and gentle ( and ) very hardworking . '' Related : Woman pleads not guilty in death of lottery winner .
Urooj Khan , 46 , won $ 1 million before taxes on an Illinois lottery scratch ticket . He died suddenly weeks later ; authorities first ruled his death `` natural '' Revisiting the case , they found he died of `` cyanide toxicity , '' a medical examiner says . The state is investigating whether there was foul play involved in his death or if it was suicide.