Part 12
Procedure
Arrest
316 Duty of persons arresting
(1) It is the duty of every one arresting any other person to inform the person he is arresting, at the time of the arrest, of the act or omission for which the person is being arrested, unless it is impracticable to do so, or unless the reason for the arrest is obvious in the circumstances. The act or omission need not be stated in technical or precise language, and may be stated in any words sufficient to give that person notice of the true reason for his arrest.
Rights during investigation - informed of belief that crime has been committed
EDIT.