How did it come from Bob's email account?
It did not - what Dave needs to do is get the IP address and information that comes with that email, and they can trace it back.
You can put any email name you want when you send out an email, just like you can put any 'phone number' out when you call someone.
If you guys think that Bob or some of us have the time to waste an hour writing lots of emails or honestly, even concerning what people do, then this troll who wrote these emails did their job. I am just surprised that Dave didn't check the facts.
And I have no problem with either Dave or Bob - each to their own, so not taking sides on their love/hate relationship