On Friday she left her home near Leslie Street and Finch Avenue East to go shopping.
When she returned home she "had some injuries on her hands and elbows, and she told her husband that while she was out shopping she had been struck by a car," said Det.-Sgt. Jim Gotell.
About an hour later she was dead.
Wu's autopsy came back inconclusive and more tests are being done to try and discover the exact cause of death.
Police are now trying to trace her steps.
She could have gone in any number of directions. Police say she often shopped at the Scarborough Town Centre — and that day she was alone.
A neighbour says Wu didn't speak English which could explain why the incident was never reported to police.
"We're checking credit card receipts, video from buses that serve the area, malls, cellphone transactions, so we know where the person was," said Gotell.
Police are also making an appeal: if a driver was involved an incident they're asking that person to come forward to help fill in the blanks and give Wu's family some closure.