They can gather more information from you. They can't gather more information from an email. It forces a decision based on exactly what the message said and no

They can gather more information from you. They can't gather more information from an email. It forces a decision based on exactly what the message said and no more - and they'd presumably want more information in order to ignore it. For a closer comparison you'd want to call from a payphone, make your report, then hang up. I have no idea if this would actually work similarly but it is at least what people do in movies when they want to provoke a police response! And it does make sense.