Let's say a psychotic alien race come across the earth.
They are technologically advanced, having near total control over matter at a molecular level, perfect understanding of biology in all its forms making them capable of manipulating and creating any possible living system, and being capable of enormous feats of astroengineering (dyson swarms, moving/destroying planets) and more. Bear in mind however, they have no significant control over the fabric of space-time (no time-travel).
Being psychotic and sadistic they want to maximize the amount of fear felt by the indigenous intelligent population (humans) but they don't just want to induce it by flooding their brains with neurotransmitters or by electrically stimulating the amygdala (both of which they could indeed do, but they just don't want to and don't ask me why: they're crazy).
In addition fear really is their thing, their sole goal is to increase it as much as possible not pain or suffering or things like that (though of course they don't mind causing such to reach their purpose), thus killing large amounts of humans goes against their intentions (you can't make dead people scared).
Further more, while indeed psychotic they behave as one, there is no in-fighting within the species and they act rationally to achieve their objectives.
So, if such a species did reach the earth in the present-day, what, using their available technology, would be an effetive method to terrify the population? And what, if any, would be the reactions of the worlds governments (besides fear)?
Note: I'd really appreciate answers that take advantage of the great technological capacity of this species...