Police claimed that they have circumstancial evidience that could link directly to the suspect, evidence gathered at the scene where Cecilia's badly decomposed body was found.
In Canada, the prosecution could not have arrested and kept in custody of the suspect if they don't have a strong case, particularly when it is a first degree, highly publicized child murder case.
BTW, it's one thing to remain objective to this case, it is another thing to demonize the Zhangs. They lost their ONLY daughter, for God sake, show some compassion!