A four-year-old girl was not poisoned by laced Halloween candy, B.C. police said Friday. But her death remains a mystery.

The toddler became ill after trick-or-treating with several siblings Oct. 31. She died in hospital of heart failure.

Some people speculated that the girl might have eaten tainted candy. But a coroner performed an autopsy and found no signs of poison in her body.

Homicide detectives continue to investigate the "unusual death," and pathologists plan to spend the next few weeks performing other tests.

Vancouver police have lifted a warning about Halloween treats. They had advised parents in the area not to let their children eat candy given out by strangers until the initial toxicology report was known.

Although an unknown medical problem is now suspected, investigators still recommend parents go through their children's loot looking for any signs of possible tampering.

No one else in the child's family became ill. It's unlikely the girl died of a severe allergic reaction, police said.