If I were at risk of being murdered, and only a cop lying could stop it, I'd want the cop to lie. Even to kids!
Let's say you’re being held hostage by a dangerous armed criminal who has already harmed others and is threatening to kill you. The police arrive, and the criminal demands to know if there are snipers positioned outside. If the cop truthfully says “Yes,” the criminal might panic and shoot you immediately. Instead, the cop lies and says, “No, it’s just us talking, let’s work this out,” buying time for a sniper to take the criminal down and save your life.
That's not what anyone means when they talk about cops lying though.
Cops can lie to suspects during questioning. They can say "your friend already confessed" or "we just got a call from the lab, your DNA matches" or "you're getting the death penalty unless you confess right now". As well as bullshit like https://en.wikipedia.org/wiki/Mr._Big_(police_procedure) (in some jurisdictions).
I'm fine with undercover cops lying about whether or not they're wearing a wire, or your scenario. I'm not so keen on uniformed cops lying to elicit confessions.
It's interesting to see who immediately jumps to a hypothetical involving the police protecting them from a crime, versus those who immediately jump to a hypothetical where they're being protected from police.
This may be irrational, but I'm more worried about being falsely imprisoned by legal means than I am about being murdered by illegal means.
That's called "exigent circumstances", and a lot of rights are normally thrown out the window if that's the case - police don't need a warrant if threat of bodily harm to themselves or others is on the table.
And that isn't what most lying cops do is about - most of the time it is bad for the public.
I'm sure we can make a framework around when they can lie. They can not lie to obtain facts or information while investigating. Doing so should poison what they gain and anything found afterwards.
> should poison what they gain and anything found afterwards.
That's a more expansive proposal than the law being discussed. The law is narrower than "investigating" and is focused only on interrogating a suspect, so presumably post-Miranda warning. And in this context being a "suspect" is a specific category elevated from being a witness or person of interest. And then the only penalty in the law is making a confession obtained as the result of a lie to a suspect during an interrogation inadmissable.
Those differences address the concerns mentioned downthread with lying in the context of undercover work.
Frankly the nickle-and-diming of when Miranda does and does not apply is itself an issue: "Oh, no, you're not under arrest, you're just being detained indefinitely," "Hahaha a dog practicing law? What an idiot, continue the interrogation," and "Your honor, the suspect failed to verbally affirm his right to remain silent; instead simply not speaking, so we were under no obligation to cease attempting to interrogate him" are all arguments that the Supreme Court has, in its infinite wisdom, seen fit to uphold as not violating Miranda.
That's an easy situation to deal with. Have someone who isn't an officer sit at the computer and pretend they are a 12 year old girl to catch a child predator and turn the evidence over to the non-lying police.
Let's say you’re being held hostage by a dangerous armed criminal who has already harmed others and is threatening to kill you. The police arrive, and the criminal demands to know if there are snipers positioned outside. If the cop truthfully says “Yes,” the criminal might panic and shoot you immediately. Instead, the cop lies and says, “No, it’s just us talking, let’s work this out,” buying time for a sniper to take the criminal down and save your life.