Link to Original Question:
How Do I Protect Myself During a Police Interview?
The answer to this question is difficult without some addition information from you. Firstly, you submitted this as a Canadian question, so I will presume you are in Canada and the investigation is being conducted by a Canadian law enforcement agency, thus I will refer only to Canadian law.
Next, it depends on what you mean by an "interview". There are two basic types of interviews with police, a "witness" interview and a "suspect" interview. If you didn't do anything wrong and just saw something happen or have information about someone else doing something wrong, you are a witness and have little to worry about. The assumption I'm going to make based on you saying "protect yourself" is that you are not a witness but rather a suspect. Statements from suspects are usually termed "warned statements" in Canada and I'll explain why later.
There are a lot of rules for police to follow when they interview someone they are investigating for some offence. These rules are almost entirely and exclusively designed to protect YOU and your rights. BTW in reference to an incorrect previous post: this is Canada- there is no such thing as "Miranda rights" here. In Canada, your rights are listed under the Canadian Charter of Rights and Freedoms. The police will read to you your "Charter Rights", which consists of the offence for which you are being arrested and your right to legal counsel, etc. (as you have probably seen on TV) but only if they are arresting or detaining you for some offence. Because you are not typing this question from your jail cell, you have not already been given your Charter Rights nor are you likely to have them read to you because your interview will be given while you are not in-custody (under arrest).
What you WILL hear is somewhat similar, and you are required to be told this- is the Brydges warning (or "police caution") to which I referred earlier. This is simply "You are not obliged to say anything, but anything you do say may be given in evidence". In other words, your statement is voluntary. You do not have to provide it nor do you have to give the police any evidence about what you did. You may not hear those words in that way, because they need only tell you it and doing so in plain language is perfectly acceptable. (Ignore what you see on Law & Order- the US laws are different).
As I said, because I'm assuming you're not typing this from a jail-cell, I'm going to make the assumption that this statement involves you going to the police station to give your statement. This is important because statements taken from suspects have slightly different rules based on whether or not you are in-custody. Almost certainly, you will be going voluntarily to the police station and you will be leaving after your statement- that is how it is done in the vast majority of statements.
That brings me to another important rule that police are obliged to follow during warned statements- you are there voluntarily and for that reason, you have the right to stop the statement at any time and leave. This is one of the biggest reasons why in-custody warned statements differ from voluntary warned statements (because obviously you can't get up and leave if you've been arrested). The police will also have to tell you about this.
The police must also tell you that you are a suspect and the offence for which they are investigating you. Don't be alarmed that they use the word "suspect" as essentially everybody is a suspect until they are ruled out. Another rule the police must follow is that they must inform you if they are taping the interview. If you are providing a warned statement, it will be taped (audio and video) without exception. The rules of evidence state quite clearly that it must be taped (audio and video) without exception or it is inadmissible. Again, that also protects you from the police stating you said something you did not- we've all seen the movies where the crooked detective stops the tape recorder, puts a gun to the guys head and says "confess or you're dead", then hides the gun and turns the tape back on. The fact that everything is on video is your assurance that nobody is going to put any words in your mouth that you didn't say.
To set the record straight on a previous posting- the rules of evidence and investigation in Canada explicitly prevent the police from lying to you about evidence. For example, the police cannot say to you during an interview "We found your fingerprints on the murder weapon" if they did not actually find your prints on the weapon. Quite simple. While the police can employ deception in other areas and ways, during your statement they cannot or they would risk any evidence (i.e. your confession or anything you told them) gained from it being ruled as inadmissible in court. In law, it is termed "fruit of the poisoned tree" meaning if the police do something improper/illegal (such as lie to you to get some information from you) then whatever evidence is garnered from that lie, and any subsequent evidence, will be inadmissible. A court trial is essentially not a trial about the accused, but a trial about how the police did their job. The police are extremely careful during an investigation to ensure that they do not violate your rights because if they did, anything they obtained in terms of evidence would be inadmissible in court. For the courts to allow it would "bring the administration of justice into disrepute".
Hopefully that gives you a little insight into the statement process. The police are simply looking for the truth. One caution I can give you is to not lie! Misleading the police during an investigation can (and probably will) result in you being charged with "public mischief" which is a criminal charge. I know for a fact that the police are far more likely to look favourably on your case if you tell the truth, even if that means that you did something wrong, than if you mislead them or flat-out lie to them. They may already know the truth and want to get your "side" of the events. While they cannot lie to you about the facts, they certainly don't have to tell you all that they know. If they already know the truth and you lie, you're not making things easy on yourself. This of course is different when the investigation concludes as during the court process the crown will have to disclose the entire police investigation to the defense. (If you want more details on this aspect, the relevant case law that sets out these rules is called R. vs. Stinchcombe)
In reference to another post that indicated that you should get a lawyer- I can say this: It is a cost-benefit analysis which depends largely on the severity of the offence you're talking about (which you haven't disclosed). If you're talking about who punched Jimmy after school or who stole the pack of cigarettes, don't bother. Lawyers are very expensive and qualifying for free legal advice (called legal aid) is almost impossible unless you are jobless and pennyless. And even then, you'll find legal aid won't represent you unless you are actually charged with an offence (which at this case you are not). The exception is that if this is a serious offence (i.e. you stabbed someone to death) then you probably should be seeking legal advice, but I don't get the impression that's what we're discussing here. In any event, at this stage- unless you or a close family member is extremely wealthy, you won't find a lawyer that will come with you to the police station. What you will get (for a lot of money) is simply advice. And the advice that you're going to get is going to be exactly what you've already received from me above (consider it pro-bono).
Obviously there is a lot more to this- in fact, literally volumes have been written on the rules of admissibility of evidence and in particular verbal statements. If you want more information on the rules of admissibility of warned statements and what the police are and are not allowed to do and say in Canada, the relevant case law that deals with much of it, is called R. vs. Oickle. It was a Supreme Court decision in about 2001 or 2002 that involved a statement the RCMP took from a volunteer firefighter in Nova Scotia that was burning homes down. It may not be the same as your situation (I hope) but how the police can act and much of what they can and cannot do is layed out quite explicitly at the end (in case you don't believe me). :) Feel free to email me if you have any other questions.