The robots came in peace. They were the last vestiges of a dead race and they carried in their silicon hearts the memories and dreams of those that built them.
It was the last wish of the last creator that the robots would go forth and tell the Universe how the creators had come to destroy themselves through hate and suspicion.
Unfortunately, they came to Earth, landed in the U.S. and were subsequently detained by the Department of Homeland Security.
Luckily, robots last a long time so for now they bide their time, sitting in their cells, every now and then chuckling to themselves.