The police have discretion on this.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
Typically, an arrest is questioned or determined if valid only after it is challenged in court. So in most cases, even illegal arrests are never challenged. Police undergo training as part of their work to know where the line is, to the extent there is one, in determining if they can arrest a person. Also, remember that police have tremendous discretion in arresting someone, so even if they can, the sometimes won't. This is the initial filter built in to the criminal justice system to avoid or remove people from the criminal pipeline.
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