A few years back the poice did their jobs based upon the assumption that has long as they did not randomly shoot a passerby for fun (in which case they might be charged with murder) they really owed no-one any particular duties that they could ever be held account for (except by firing).
This changed a few years back when a Court in Toronto held that the police could be held responsible by the victims of a rapist where the police did not take steps to warn potential victims of a danger.
Now the Supreme Court of Canada has held that the police have no particular protection from, and can be liable to, innocent suspects who they negligently investigate. Thus an investigation that is negligently carried out and thus results in harm to a person can give rise to a law suit against the officers (and their employers) who carrried out the faulty investigation.
While in the particular case at hand the Court held that the investigation was up to snuff, it is only a matter of time before a police force is held liable for a negligent investigation and the harm caused. Where this will get really interesting is where the police are faced with balancing their duty to potential victims against their duty to potentially innocent suspects. Fundamentally though this is a good ruling in that it affirms the idea that people who are given significant powers are not put above the law just so they can be free to use their powers -- like all of us they have a duty to act reasonably as called upon this circumstances. As the Chief Justice in the majority judgment said:
3 I conclude that police are not immune from liability under the Canadian law of negligence, that the police owe a duty of care in negligence to suspects being investigated, and that their conduct during the course of an investigation should be measured against the standard of how a reasonable officer in like circumstances would have acted. The tort of negligent investigation exists in Canada, and the trial court and Court of Appeal were correct to consider the appellant’s action on this basis. The law of negligence does not demand a perfect investigation. It requires only that police conducting an investigation act reasonably. When police fail to meet the standard of reasonableness, they may be accountable through negligence law for harm resulting to a suspect.