[Avodah] pressuring witnesses

[Ben Waxman]

Anyone who watched Shababnikim saw the episode in which the police 
investigator threatened to reveal to a web site embarrassing information 
about a yeshiva bachur if the bachur didn't provide the detective with 
information about a crime.

According to Halacha is this technique kosher? Would shotrim working in 
the framework of a Sanhedrin be allowed to use it? Does it matter what 
the crime was (in this case it was arson)?

Ben