ATC would have known that it was either a false alarm or that the highjackers knew every nuance of what pilots are to say to subtly confirm or refute a suspected highjacking. The latter is far less likely than a malfunction, but cannot be ruled out with certainty by radio communications. Whether the police understood that or not is another question, as they have a different mindset (remember the FBI's insistence that TWA800 involved a bomb, despite no evidence at all supporting that hypothesis).

Once the plane was safely on the ground, less drastic measures might have been in order.

This looks like a typical case of testosterone laden police looking for an opportunity to show off their weapons.