In the US and England, police have broad powers to arrest and detain suspects. In Canada police supposedly do not have that power. In a crime that gets a lot of publicity, police will sometimes detain a suspect for a period of time, then release them with no charges filed. Somehow the news media is informed of the release and a swarm of reporters and paparazzi are there to take pictures for next day's tabloids. Generally this is for a day or two in England. In the US it can be up to 72 hours. This process encourages the public to think of suspects as guilty, trusting the police would not arrest innocent people. This is sometimes called "rounding up the usual suspects". Sometimes police will call a suspect a perpetrator or person of interest and question them without giving a Miranda warning. This is a technicality since in the US police are required to give a Miranda warning if arresting a suspect. If after arresting and then questioning a suspect, police may decide they have the perpetrator. Then they will hand the case over to the district attorney.