Well since they can lie to you and say anything they like bordering on blackmail, you need to know that. You have to be smart enough to guess what they know and have the fortitude to refuse to answer and ask for a lawyer continuously, sometimes possibly for hours. Always be respectful but resolute on getting that lawyer, no reason to piss them off any more than you are by refusing to answer their question. Police can be quite violent and volatile just like any human perhaps more so since they have almost all the power and guns in a given situation.