After a crime has occurred the police begin an investigation to try and discover evidence about it. This is a careful process that involves many different elements. Detectives will collect physical items such as weapons, footprints and blood samples, and send them to labs for testing. They will also record and document electronic data such as online searches and communications. They must use gloves to avoid contamination and follow strict procedures for collecting physical and forensic evidence, ensuring an unbroken chain of custody from the scene to presentation in court.
They will interview witnesses, and in some cases the victim. This could be in person or on the telephone. An interpreter can be used if needed. Police will look for CCTV footage of the area and if possible recreate the crime scene using digital software. They may also conduct surveillance on a suspect, but not unless they have reasonable grounds to believe he or she has committed a crime.
If they are confident that they have sufficient evidence to charge a suspect, the police will submit their findings to the prosecutor for a decision on whether to charge that person. The prosecutor may decide to investigate further, charge the person or stop the investigation.
The police will continue to follow all reasonable lines of enquiry until they can prove their case beyond reasonable doubt or there are no viable lines of enquiry left. This will often involve returning to the scene, re-interviewing witnesses, conducting forensic investigations and serving search warrants.
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