What Yieldmap is talking about is known as 'spoofing'. Anyone who has a routing hub can set set the IP address to any address they wish, at any time they wish, and make the message appear as though it came from that IP address. If someone has your IP number they could send a message that looks like you sent it, I have seen this done before. This could draw into question any results of an investigation of this type.
Have a good day!!!
Andy