I agree that the prosecutors are probably guilty of some kind of misconduct. However, I think the email you quote is the kind we would see either way. We expect prosecutors to be unabashed in their pursuit of convictions - it's their job. They should cajole and berate, in turn, people who help or hinder their cases.
That may be a shitty model, but it's the model we use. We have a responsibility to only punish people for things they knew to be wrong - thanking a lab tech for a favorable result doesn't cross that line.
That email, unless pleasantries or enthusiasm count as bribes, would not be considered a bribe. It's just good practice to be polite to those who can help you. Perhaps we should legislate that prosecutors should be dour towards everyone they encounter, less a pleasant experience bias someone?
P.s. I realize that improper conduct by both parties is probable in this case, but the quoted email certainly does not cross the line.
Why should prosecutors ever be in direct contact or even know the people running the actual tests? Except in cases where the lab must testify, in which case there should be separate controls (perhaps someone else runs the tests).
Allowing prosecutors to "do their job" and try to be polite or have any influence at all on what's supposed to be a purely factual system is completely and utterly wrong.
That may be a shitty model, but it's the model we use. We have a responsibility to only punish people for things they knew to be wrong - thanking a lab tech for a favorable result doesn't cross that line.