Symposium: Carpenter and the eyewitness rule

One of the most basic ideas in Fourth Amendment law is what you might call the eyewitness rule: The government can always talk to eyewitnesses. If the police find out a bank was robbed, they can go to the bank and interview those who saw the crime occur. They can talk to the bank clerk about what he observed. They can talk to the security guard about what she experienced. They can talk to bank customers about what happened. These interviews, whether voluntary or compelled, don’t trigger the Fourth Amendment. There’s just no Fourth Amendment right to prevent people from talking about what they saw you do.