3. Understand the evidence in your case

In cases where the Crown says you were over the legal limit, the Crown must prove how much alcohol or drugs you had in your blood. They do this by using reports about the breath tests or drug tests as evidence. In some situations, you might be able to argue that the tests were not done properly, but this is very difficult to do.

Police use a breath machine to test how much alcohol is in your body. Usually, the breath machine is at the police station. The breath machine must be tested and calibrated properly.

Screening devices allow police to check your breath at the roadside. These devices tell the police if you are over or under the legal limit, but they do not tell the police exactly how much alcohol is in your body. To know exactly how much alcohol is in your body, the police take you to the police station to be tested with a breath machine.

If the police believe you have drugs in your body, they can ask a drug recognition expert to come check you out to decide if they should test you for drugs.

To test for drugs, police usually take samples of your body fluids at the police station. Bodily fluids are things like saliva, blood, or urine. Those tests require specialized training so they are done by a certified drug-recognition expert. The body fluids must be handled carefully. There are some screening tests for saliva that the police can use at the roadside instead of taking you to the station.

Other evidence

Examples of other include:

  • a witness who tells the judge what they saw
  • the opinion of someone who is an expert in understanding blood-alcohol levels or blood-drug levels
  • videos of your and breath tests


The Crown must give you a copy of all the evidence they plan to use in your case. The copy you get is called “disclosure“.

The Crown will normally give you some disclosure inside the courtroom the first time you go to court. Often you won't get all your at once. You may have to go back to court a few times before you get it all.

Review any disclosure you get and look for important items, including:

  • a police summary of the case
  • reports from your alcohol or drug tests
  • police officers' notes
  • witness statements
  • photos or videos

If you think something is missing from your disclosure, you can write a letter to the Crown to ask for it. Then on your next court date ask the Crown if they have your missing disclosure.

You have the right to get your disclosure before you decide whether to or set a date for . You should tell the judge in court if the Crown is not giving you disclosure that you asked for.

After you review your disclosure, you can decide if you think the Crown has enough evidence to prove you're guilty .

It's a good idea to have a lawyer review your disclosure with you. Even if you think the Crown has enough evidence about what happened, you may still have a legal defence.

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