I got interviewed once (many years ago) as there was an allegation made against someone I was with. Given that I neither reported a crime, nor left the scene, that left me dragged into the investigation.
I was a minor at the time, but had nothing to hide, and so went down to the station, told them what had happened from my perspective (no lawyer or parents present) and then accepted the offer of a lift home from them.
I'm pretty sure the real interrogation was on the trip home. The cop was very friendly, and was constantly trying to position himself as being on my side, making some mildly derogatory comments about the complainant, and seeing if I'd agree.
Nothing would have been admissible from it, I'm sure, but people who suggest you don't need to worry about talking to the cops unless you have something to hide are kidding themselves.
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Just in the interests of balance, my other engagement with police (apart from when I tried to join them once...lol) was with the New Zealand police when I got completely drunk, and decided to sit on the kerb about 100 metres from my apartment, as I was a little weary.
They were extremely polite (given circumstances) and walked me home. Got me off the street, kept me safe, and meant other citizens weren't subjected to me throwing up on their shoes, or anything.
Funniest part is that they wanted to see my license so they could make sure my address really was close by before walking me home. But of course I have an Aussie license. I'd lived in NZ for about a year at that point, and it had taken the edge off my accent, but I got a very direct message of 'If we start walking you home, and it turns out you live in Melbourne, you know we're going to be unhappy, right?'