[anymouse]

Yes it does somewhat look like left-handed writing, but with odd irregularities to the consistancy of letter structure. So I bet it was a right-hander lettering it with his left hand.

For a muslim to write using his left hand is very offensive, but a sick bastard terrorist would take purverse pleasure in the irrony of doing so to commit this type of bio-terrorist attack.

[stlnative]

Well hopefully they can pick up a partial print off the back of the self-stick postage stamp if they did not use gloves.
Maybe DNA off the envelope seal, if they licked it closed, but I doubt it.

[Ymani Cricket]

What do you make of the hyphen between St. Petersburg and FL?? And the dot (.) after FL which is no longer used in state's abbreviations? (officially anyway)

[stlnative]

Also it looks like they used a marker instead of a ink pen?
Do you agree?

[Ymani Cricket]

So I bet it was a right-hander lettering it with his left hand

I disagree. Did you consider a person who is normally used to writing from right to left (as in Arabic). By the way, I am left-handed.