It's not quite that. The police don't HAVE to write everything down, or record everything, etc. And they're anti-aligned with you. So things you say in custody

It's not quite that. The police don't HAVE to write everything down, or record everything, etc. And they're anti-aligned with you. So things you say in custody can and will be used against you, but not everything you say can be used in your defense. Which is why you should never talk to cops without your attorney, especially if you're being arrested.