not aliens.

they are demons.

If the FBI says so it must be true, right? I mean they only work for our benefit don't they?

It's kind of obvious that aliens are not physical beings from other planets. They've been around for thousands of years, at least, under other names (gods, angels, fairies). They can come and go in the blink of an eye, and seemingly pass through solid objects. They defy the laws of physics. Hypothesizing them as inter-dimensional doesn't seem unreasonable given these observed facts.

This has been my theory.