The victim's relatives hint at family squabbles. And Khan's wife, Shabana Ansari, has endured clutches of reporters outside the family home and business, asking even whether it was a lamb or beef curry dinner she made for Khan on the night he died.
"She's just as curious as anyone else to get to the bottom of what caused her husband's death," said Al-Haroon Husain, who is representing Ansari in the case that will divide up Khan's estate, including the $425,000 in lottery winnings.
Ansari and other relatives have denied any role in his death and expressed a desire to learn the truth.
Authorities remain tightlipped about who they may suspect. In the coming weeks, they plan to exhume the 46-year-old Indian immigrant's body, which might allow investigators to determine exactly how he was poisoned and to gather more evidence for any possible trial.
Khan seemed to be living the American dream. He had come to the U.S. from his home in Hyderabad, India, in 1989, setting up several dry-cleaning businesses and buying into some real-estate investments.
Despite having foresworn gambling after a pilgrimage to Mecca in 2010, Khan bought a ticket in June. He jumped "two feet in the air" and shouted, "I hit a million," he recalled at a lottery ceremony later that month.
He said winning the lottery meant everything to him and that he planned to use his winnings to pay off mortgages, expand his business and donate to St. Jude's Children's Research Hospital.
He was just days from receiving his winnings when he died before dawn on July 20.
The night before, Khan ate dinner with his wife, daughter and father-in-law in their house in Chicago's North Side neighborhood of West Rogers Park, home to many immigrants from India and Pakistan.
Sometime that night, Khan awoke feeling ill and collapsed as he tried to get up from a chair, his wife has said, according to the Chicago Sun-Times.
"I was shattered. I can't believe he's no longer with me," a tearful Ansari, 32, told The Associated Press in an interview Tuesday.
With no outward sign of trauma, authorities initially determined Khan died of natural causes. But a concerned relative whose identity remains a mystery came forward with suspicions and asked authorities to take a closer look.
Further toxicology tests found a lethal amount of cyanide in his blood, leading the medical examiner in November to reclassify the death a homicide. The Chicago Tribune first reported the story Monday, and reporters descended on one of the family's dry-cleaning businesses.
The revelations followed, instilling the family tragedy with soap opera-like suspense that even attracted reporters from overseas.
Khan died without a will, opening the door to a court battle.
Under Illinois law, the money should be divided evenly between his wife and daughter, but Husain says the man's three siblings kept asking whether they had rights to the money. In their filings, Khan's siblings accused Ansari of trying to cash the lottery check and expressed concern his daughter would not get her fair share.
A judge has made Ansari the administrator until a ruling on how to divide the assets.
Khan's sister, Meraj Khan, and her husband, Mohammed Zaman, told reporters Friday that they had no suspicions before the fuller toxicology results showed cyanide poisoning.
Zaman then added yet another puzzling wrinkle: Ansari is a vegetarian and therefore would not have eaten the lamb curry she prepared for her husband the night he fell ill. Ansari has repeatedly said she, Khan, her father and Khan's daughter all ate the same meal.
Authorities have not said how they think Khan ingested the cyanide, which can be swallowed, inhaled or injected.
Detectives questioned Ansari for more than four hours at a police station in November and searched the family home.
Around the same time, Ansari's stepdaughter, Jasmeen, decided to go live with Khan's sister, who had won guardianship of the teen.
"Of course she was upset," Husain said of Ansari's reaction. "At the same time, I think she wants to move forward with her life. ... With her stepchild, her in-laws, she doesn't want to really have anything to do with them. There's some great animosities between the two."
And then there's Ansari's father. A few months before Khan's death, two federal tax liens were filed against his father-in-law, Fareedun Ansari. He owed $124,600, according to the Cook County Recorder of Deeds.
Finally, Khan's ex-wife and Jasmeen's mother emerged. Now remarried, living in South Bend, Ind., and going by the name of Maria Jones, she told the Chicago Sun-Times she last saw her daughter 13 years ago, when she says Khan took the girl to India. The distraught woman said she didn't know the girl was in the U.S. and she hoped to reconnect with her.
"I don't know if she knows I'm still alive," she told the newspaper, sobbing during a phone interview. "I thought she was in India all these years."