Ask any criminal lawyer for the most important piece of general advice to give to someone who has just been arrested, and this is what it will probably be: Don't say anything until you have talked to a lawyer.
When the accused talks to a lawyer, he will likely be advised not to say anything to the police. He is not obliged to make a statement.
Statements made to the police whether they be confessions or exculpatory statements, i.e., explanations of alibis are generally admissible in court provided they have been legally obtained. An exculpatory statement can be just as damaging as a confession in the long run if the police can prove it was a lie.
The Canadian Charter of Rights and Freedoms requires that the police inform someone who has been arrested or detained of certain basic rights.
Everyone has the right to be told why he has been arrested or detained and that he has the right to retain and talk to a lawyer without delay. The police cannot question the person until he has been given a reasonable opportunity to retain and talk to a lawyer, unless he clearly and explicitly declares his intention not to reach a lawyer.
When a person does make a confession or an exculpatory statement, to be legal it must be voluntary. In old movies, we can see the police shining a bright light in the eyes of the accused, or not letting him go the bathroom until he confesses. These sorts of practices are not acceptable any more if they ever were. The police cannot threaten or frighten a person into making a statement. Conversely, they cannot promise him lenient treatment or some other form of benefit in exchange for a statement.
Illegally obtained evidence, such as an illegally obtained confession or an illegal wiretap is not automatically excluded from a court case. Generally speaking, however, confessions that have been obtained by breaching a Charter right of the accused have been declared inadmissible as evidence. Both guilty and innocent people try to talk their way out of the police station. Few of them succeed.
There is no doubt that the best general advice is to wait for a lawyer before saying anything. For those who have done nothing wrong, a lawyer will sort it out for you eventually, and the risk of talking yourself into further trouble disappears.