> like if the cops arrest me and ask where i was last night and I don't tell them i was having dinner with their chief's wife (and thus not murdering mine), does that mean i absolutely cannot use that fact as part of my defense if my lawyer decides during trial it might be a good idea?
The issue is that a prosecutor may use the omission of certain facts during your interrogation as a way to cast doubt on your intentions or character. It's a very common tactic.
>do u at least have the right to have a lawyer present when you're being questioned like this?
https://www.gov.uk/arrested-your-rights/legal-advice-at-the-... explains things quite well. IIRC you're obliged to identify yourself when questioned but don't have to give any other details. You then have the right to legal representation, a free independent lawyer is provided on request if you don't have one.
I don't think we have a complete right of silence without - for example - being found in contempt of court.
It won't result in contempt of court, but it will result in a direction to the jury that they're entitled to consider unsupported statements you've made in court (but not earlier) as false.
The issue is that a prosecutor may use the omission of certain facts during your interrogation as a way to cast doubt on your intentions or character. It's a very common tactic.
>do u at least have the right to have a lawyer present when you're being questioned like this?
In the US? Always.