The police can stop someone if they witness that person committing an offence, or if they believe that the person has just committed an offence.
Someone stopped by the police has the right to remain silent and refuse to answer any questions. One of the few limitations on that right is that the police can require an individual to take a roadside breath test without talking to a lawyer first. Still, someone who has done nothing wrong is generally better to co-operate with the police, at least to the point of self-identification. In certain cases, one who refuses to say anything could be charged with obstructing the police, and of course anyone who gives the police a false name could be guilty of mischief, to say the least.
If the police continue to ask questions and refuse to allow an individual to leave, they can be said to be detaining the individual. Anyone being detained has the right to know why, and to speak to a lawyer, and is best to remain silent until advised by a lawyer, because anything said to the police can be used in court.
Police may search a person they believe has committed an offence involving weapons, as well as anyone they arrest or have grounds to arrest, whatever the charge. They can also search anyone who consents to being searched. Furthermore, if in searching someone they have arrested on one charge the police find evidence of a second offence, they may charge the individual with that offence as well.
In certain situations, the police may obtain a search warrant, however they are unlikely to obtain one prior to attending a protest or demonstration. As discussed above however, they can search if they lay a charge, and in some cases might lay a charge – especially a charge of one of the generally worded offences that can be committed on the spur of the moment just to be able to conduct a search.
While conducting a search, the police may also seize items that may reasonably be evidence of a crime, however they may not otherwise seize personal property without a search warrant. Sometimes, evidence such as film footage can even be seized at a later date if the police can convince a judge to issue a warrant on the basis that such evidence is relevant to a charge that has been laid, even against someone other than the one to whom the evidence belongs.
The police may enter a home if they have a warrant or permission, or if they are pursuing someone they believe committed a serious crime and is inside the home, if they believe someone inside the home is about to harm someone else, or to provide emergency aid.
Section 8 of the Canadian Charter of Rights and Freedoms protects against unreasonable search and seizure, and if a search, or seizure of evidence, is found to have been conducted by the police in an unreasonable manner, the evidence found may be excluded and the charge itself may even be dismissed. However, that protection only arises in court, and at a later date. Unfortunately, the best course of action if police wish to conduct a search is probably to allow them to do it, but to state “I do not consent to this search” while they're doing it, and to challenge the legality of it later, if appropriate.
One may be charged by either the police or a member of the public, if observed committing an offence or apprehended right after doing so.
The police usually arrest and lay a charge, but in some cases if an offence is minor, will lay a charge without arresting. Someone who is arrested is taken directly to the police station, whereas someone charged without being arrested is simply required to appear in court at a later date. Obviously, failure to appear in court at the appointed time is a crime in itself.
If the police do arrest, it is usually because they perceive the offence to be more serious. The police are required to read rights to a person they arrest, including the right to remain silent, the right to be told the reason for the arrest, the right to hire a lawyer or to locate one free of charge through legal aid or the duty counsel system, and the right to speak to that lawyer as soon as possible. The person is then taken to the police station, fingerprinted and photographed. Sometimes, the person is invited to be interviewed on video, which of course is the same as making a written statement, and generally not a good idea prior to speaking to a lawyer.
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