During the DC Beltway sniper shootings, the authorities were constantly PSA-ing the public about the need to watch out for a white van (which turned out to be inaccurate.) The snipers weren’t using a white van (which may have been the intention of the authorities, to make the snipers feel “safe” and let down their guard,) but if they had, wouldn’t they simply be watching the news and think, “OK, guess we had better start using a different vehicle instead?”
(Brought to mind by the recent Austin package bombings. Seems like when the authorities PSA the public about the bomber’s methods and tactics, that’s just telling the bomber indirectly that he needs to change his methods.)
A smart authority would consider this, of course, and be strategic about exactly what info is released.
But there are reasons to alert the public, even if the perp is also likely to be alerted:
First, the perp may not get the message before attempting another crime, so the warning could be accurate and useful;
Second, if the perp does hear the PSA, now they have to find a different method (or at least another colored van). That’s one more step to make it harder for the perp, and it’s more likely they’ll screw up with a different method (after all, PSAs only go out if the perp was successful with their first method; so chances are, they’ll be less effective with a different one).
In the case of the DC sniper, they were caught when authorities released the details of the correct vehicle and a trucker noticed it parked at a rest stop. The advantage of having more people on the lookout for a person or vehicle usually outweighs the downside which is the many false reports the police have to sift through. Police usually will not release information that they think the criminal does not know they know.
There is also potential civil liability for the police if they have very clear information about the bad guy’s activities and the risk posed to the public, yet do nothing to warn people at risk.
For example, some time ago in Ontario, the police knew about a rapist with a very specific MO. He would climb up to the balcony on appartements on the first floor, having cased it to know that the occupant was a single woman, and rape her. He operated in a very clearly defined range of neighbourhoods in Toronto. The police even called him the “balcony rapist” in their internal documents. They didn’t release any of that info to the public, in hopes of catching him by monitoring the specific type of apartment buildings.
One of the women who was raped, after the police knew all this detailed info, eventually sued the police, arguing that the police weren’t protecting her. They were using women like her as bait, pretty much like little lambs tied up in the jungle to attract a tiger.
She won a quarter million from the Toronto Police in her court action.
Oh, and the police advanced exactly the point made by the OP, saying they didn’t want to tip him off.
The plaintiff, Jane Doe, had pieced enough together that she was putting up signs in the neighbourhood warning that the balcony rapist was in the area.
The police threatened to charge her with a criminal offence for interfering in a police investigation - by trying to warn people at risk of a criminal attack. :rolleyes: