It's modern day, and aliens travel to Earth (cloaked so that no one is aware of them). They send huge robots down to a town or city and manage to kill everyone there, apart from a single survivor.
This survivor manages to make it to another town, where the first thing he does is run to the police station to tell everyone there that he has witnessed the destruction of the town/city and managed to escape.
However, everyone looks at him as if he is crazy. They say "if that had happened we would have heard about it!"
So what would be the best way for the aliens to ensure word isn't spread about the destruction of this town/city?
The aliens have almost omnipotent powers with their advanced technology compared to ours. They can do things such as cloaking, holograms, blocking satellite/radio/internet communication and anything else you can think of that technology can do now or in the future. However, they cannot erase memories to make everyone think that the town/city never existed.
The ruse only needs to go on for approximately 24-48 hours, after which time they have already destroyed a number of smaller towns/cities in order to make bases for themselves where the towns/cities once stood. After this time they will drop the stealth tactics and branch out from these bases to attempt to subjugate the human race.
They have studied Earth for a while and understand our technology limits and humans themselves, so they wouldn't leave any means to be discovered by accident, until they're ready to reveal themselves.
What would be the best way for the aliens to make sure no one has noticed these towns/cities have been destroyed? They will have to take into consideration people who live there all of a sudden not communicating with out of town friends/family, people who would drive through after the town is destroyed potentially walking into the ruins.
What size towns/cities would be big enough to have bases of operations but small enough to not attract attention to the general population? Could it happen to a small city or would it have to be small villages? What countries could they be in that it would go unnoticed?
How would they subvert things such as satellites noticing this has happened?
To clarify: Perhaps I put too much information into the question, so I will summarize what I am asking.
If you had infinite technology, how would you conceal the fact you have captured a town and all of its people without alerting anyone for 1-2 days?
It's OK if people start to suspect something is wrong (like a friend going to voicemail who usually picks up), but without anyone jumping to the conclusion that the planet is being invaded.