Sure as heck took them a long time to investigate.
I mean, that's what we do in the civilized world. If someone is accused of a crime, police need to investigate every single nook and cranny of the accusation before pressing charges to ensure a crime was actually committed, even if that takes years.
In the case of sexual assault, the crime is often extremely hard to prove. I know an OPP officer who used to work in the sex crimes unit. From what I've heard, there's often little to no physical evidence that an assault occurred and, equally often, the victim may take years to come forth, by which time there is no evidence and a case cannot be pursued -- not because the police don't believe it happened, but because there's 0% chance of proving it happened.
Also, unlike other crimes, there are usually no witnesses to sexual assaults, and he said/she said doesn't hold water in court.
Even when police do successfully lay a sexual assault charge, a good percentage of the time that charge gets thrown out or stayed during the preliminary stage because the evidence the Crown has just isn't strong enough to persuade a judge that the case should continue.