If they're talking gamma rays they aren't talking about lasers....perhaps (if there is any truth behind this tale) some sort of nuclear device could emit gamma radiation and kill someone (actually that really happened to a spy in Russia a couple of years ago - he was exposed to some sort of radioactive substance put in his drink and died a couple of weeks later).
So yes gamma radiation (from a radioactive substance) could kill a person, even within a few minutes if the dose was high enough, but it would have to be delivered some other way than in a beam. Heck, it's tough enough to try and make an X-ray laser, and there's no way you could carry it in a violin case! For one thing, such high intensity radiation is tough to focus - especially in a way that could hit one person in a crowded room and not injure or kill others around him. What would you use for an output mirror for gamma rays?!? I have no doubts the CIA could kill a foreign spy with radiation, but not with any sort of a "laser rifle".
Also, the first scenario is pretty bogus as well. It is not uncommon for an electric livestock fence to run 10,000 volts, but there is practically no amperage. Think about it - if there was enough juice in the fence to kill a man and fry his private parts, then any poor cow or sheep unfortunate enough to touch the fence with its nose or ears would have those parts burned off and it might even die. That would mean your milk would be scalded if they were diary cows and if beef cattle your steak would be cooked well done WAY before it ever got to the slaughterhouse! Total urban legend on that one.
). Talk about sending a message though... Not the subtlest of poisons! Three weeks to die from a highly traceable radioactive isotope that is only produced in a handful of places on earth? I mean, c'mon... !