Most times I meet with clients, I ask them about their interactions with the police that investigated them. Most of the time, people who I'm representing chose to speak with the police. Now, given that I am representing them, there is certainly an argument to be made that there decision was not a good one.
I think people choose to speak with the police for many reasons, but a few spring to my mind: 1) People want to be liked, and they think if they are cooperative, the officer will like them more, and be less likely to arrest them; 2) People think they have to, and they will get in trouble if they don't; 3) People think they did nothing wrong, and that if they explain the situation, they can talk the officer out of arresting them; and 4) People are apologetic, and think it they apologize and confess, things will go easier for them.
All of these reasons are wrong. 1) I think that the police are trained to arrest those who commit crimes, whether they like them or not. 2) They also don't "have to" cooperate with the police, other than simple requests like providing identification/registration/insurance when driving a car, and can't get in trouble for talking to the police. 3) People who think they did nothing wrong often are ignorant of the law, and end up confessing to something they did not even know was a crime. 4) Save the apologies for the judge, the police are in the business of gathering evidence of a crime, and can't let you off. I've had many times that my client's admissions ended up being the only admissible evidence in a case, and without those admissions to the police, we would have won their case.
The other thing that comes up at times, are the things police officers tell someone, in order to get them to talk. I hear all kinds of things that the police promise, or trick someone with, and often times they are successful in procuring information from my clients that is later used against them. In fact the police are allowed to lie to an accused criminal, in order to secure a confession or evidence. While this is not allowed in civil cases, it is allowed in criminal investigations.
There was recent article in the Seattle Times (click here) where a federal appeals court ruled that police cannot use a "ruse" or fancy name for a lie, in order to trick someone into providing information in administrative cases. In that case, the police had lied to someone they were investigating for social security benefits, and told them they though they were a victim or a theft, in order to gain their cooperation and secretly film their movements. In this case, the police were investigating them not for a criminal act, but for an administrative issue.
While this was not allowed in this administrative case, it likely would be allowed in a criminal case, and the takeaway is that no one should interact with the police for any reason. They should seek legal counsel if ever contacted by the police, and remember that the police are the investigation unit of the prosecutor's office.