He's trying to get you to come in and give a statement before you have a chance to review the evidence against you or consult with an attorney. He knows that if he can commit you to a story or catch you in a statement that contradicts your other story, someone else's story or some piece of evidence it will help in your prosecution.
Detectives with strong cases try to get the target of the investigation to confess. So do detectives with weak cases.
Why? Because if the detective gets a confession it makes the prosecution's job much, much easier.
A person who is asked to come down and tell their side of things should immediately go get themselves the best criminal defense lawyer they can.
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