The internet has drilled into our heads that if you’re being detained by the police, you shouldn’t say anything other than “I want a lawyer.” But in a non-custodial interview, how can you know if you’re considered a witness or a suspect? Obviously, the police need the cooperation of witnesses but it is also well established that the police can lie to get to the truth.
So how do you know when to talk and when to clam up?
When you know whether or not you have something you don’t want them to know.
The problem then may be that they don’t know whether that something is of any relevance to what they want to know - and you might not, either, even if you’re not in any way guilty of what they’re investigating.
If you don’t want to be a suspect, don’t behave suspiciously.
I’m not sure how it is in other jurisdictions, but in mine (Germany) a suspect has to be informed by the police of being a suspect. Obviously, that status can change during the course of the proceedings; you might be questioned as a witness at first, and then during the investigations police might begin to suspect that you could be involved as a perpetrator. In that case, police have to inform a suspect of suspect status as soon as that person becomes, for them, a target in the investigations. So they cannot investigate you while pretending that they merely regard you as a witness.
Are you sure of that? I live in Germany too and never heard of that provision. Never had any contact with police either (except the usual Meldeamt and car registration paperwork), but it sounds too good to be true. It’s almost like if they had to warn you that they know there is something fishy about you which would seem to me to allow the suspects to destroy evidence. And do you happen to know how they decide where the line between strange 
and suspicious 
lies?
No. Even if you are confident that you know nothing of value, regarding the immediate investigation or generally, you cannot trust that the police are evaluating you from a position of neutrality. There are endless anecdotes about police deciding in advance where their primary suspicions lay, and then manipulating circumstances to ensure the outcome matched their hunch, evidence be damned. This much is objectively true; discussion of why this happens, and to what frequency, takes us out of GQ and into debate territory. But the simple truth is, one’s innocence is largely or entirely irrelevant when dealing with law enforcement.
Incorrect and unhelpful. The police form their suspicions for their own reasons. Your attempts to portray yourself as above suspicion may actually backfire.
The most objectively true answer is, you should always have an attorney present in anything but the most transitory and casual interactions with the police. The attorney may not do anything but observe to ensure the police are properly following procedure and respecting your rights. And you can even say that directly: “I haven’t done anything wrong, and I will be happy to cooperate and speak freely about this incident/case/whatever. But in my own interest, and in the interests of your case being conducted properly so its findings can’t be challenged on procedural grounds, I require an attorney to be present.”
The provision is section 136 of the Code of Criminal Procedure (Strafprozessordnung, StPO). There is case law that holds that the line between suspect and witness is drawn where the investigations of the police are directed against that person; if that is the case, then you have to interrogate the person as a suspect (“Beschuldigter”), not as a witness, and inform them accordingly. If need be, that can lead to a duty to inform in the middle of an ongoing interrogation, which would mean the status of the person changes on the spot. Here is an example for a case along these lines.
(Both links in German - apologies to the non-Germans here for the digression into this particular jurisdiction)
Thank you very much, I had no clue.
ETA: Reading the links I would like to clarify that the police has to inform the suspect that he is a suspect only if/when they interrogate him, I had wrongly assumed that they had to inform him already when the suspicion arose.
Getting the police to use the word “suspect” is the trick. “She/he is just a person of interest” is heard quite a lot nowadays.
I’ve read that one key giveaway is if the questions are all about you. If they’re asking where you were and what you were doing, you’re probably the suspect. If, on the other hand, they’re asking all about your friend Bob and what he was doing, then you’re probably just a witness.
It’s still possible, though, that by asking about Bob, the cops are in fact indirectly trying to coax information out of you (the suspect.)
The other thing, of course, is whether you are in fact guilty of a crime and know it (although as others pointed out, plenty of innocent people get suspected of a crime).
The only time you should talk without an attorney, IMO, is when they can give you signed blanket immunity, signed by the DA. They will give such a letter if they believed you had great witness information.
YOU can never benefit from talking to police with an attorney.
I bet you forgot the “out” on your “with”. Kind of changes your meaning. 
Try out your theory when the police approach you with a picture of somebody, and say, “This is an at-risk person who is missing, but may be in this area. Have you seen this person?”
And then report back how the encounter goes.
Assuming you mean “without an attorney” , I also assume by “never” you meant something more limited- surely, you don’t mean that if my car is stolen with my child inside, I’m better off finding an attorney and waiting for him to get there before talking to the police. Or that I need to wait for an attorney to tell the police which hallway the person shooting up my office is in. Or that I need to hire and wait for an attorney to report that I am the victim of any crime. And I should call for an ambulance on my cell phone even though the police officer two feet away from me can probably get a faster response.
You may not mean those things- but that’s actually what “never talk to the police without an attorney or a signed immunity agreement” means - and saying that isn’t helpful to people who are trying to figure out when they should or shouldn’t talk to the police.
That’s really interesting; thanks for sharing! Definitely not the case in the U.S.
Another complicating factor is that it may not be you who did something wrong, but if you helped cover up someone else’s wrongdoing (perhaps without even fully realizing what you were doing at the time), you may be charged as an accessory after the fact. Talking to the police in that case is tricky, because the longer you go on helping the person cover up the crime, the worse it may get for you, but immediate and full cooperation with the police doesn’t guarantee you’ll be off the hook. Definitely time to call a lawyer.
No, no, no, no to this.
You can be completely, 100% truly innocent and can still be caught up and convicted of a crime. Even executed for it. The article below came out yesterday. Do not talk to the cops. Period. Some caveats are being a bystander to an accident or crime (as in…you are on the corner as a pedestrian). Otherwise STFU.
The caveat is: will you know exactly when the police go from “taking a report from a distraught parent” to "prime suspect in murdering their own baby’? Let me give you a personal example apropos to this. As my daughter lay dying, my wife felt responsible. Police were there in the hospital and my wife made it clear that as soon as I left to meet my mom in the parking lot she would turn herself in to the police. I told this to the police and asked them not to listen to her if she did that. Was it stupid to do that? Of course it was but I mean our daughter was dying. You don’t think right when under that much stress. My point is that later when I read the police report, that one statement made ME a suspicious party and they officially ruled me out of the incident when they confirmed that I was at work 50 miles away when it happened.
tl;dr: Never talk to police.
Not to pry but not following that story:
Not trying to be a jerk but I am not following that timeline.
I am sorry for what happened to you - but in your story, your daughter was in the hospital, not in a car being driven by a car thief where a delay in giving the police information would likely result in a delay in finding the child. There’s a reason my example was one of an ongoing crime.
I think reporting a crime is a different thing. You pretty much have to talk to the police to let them know something bad is happening.
I am also not following your story. You shouldn’t talk to the police because they briefly considered you a suspect but then confirmed you were 50 miles away? So, what was the harm in you talking to the police? They did their job, investigated, and found you were not involved.