If no one has ever came across into our universe then how have they placed parts of the device in our universe and they even know the co-ordinates of the device parts? The device is the one that Peter can only trigger and that can devastate our universe and save their universe.
No one placed parts of the device in our universe.
I'm not sure how much of Fringe Season 3 you have already seen, and so I will use spoiler blocks liberally.
You are making two incorrect assumptions:
- that the device was created some time before the present;
- that the device, or pieces of it, were placed in our universe by agents from the parallel universe.
We find out in the episode "The Day We Died" that the machine exists in a
There are no so-called
"First People" who designed and built the machine.
Walter is the designer of the machine, and he sends it back in time through a wormhole.
He sends the machine
to the distant past before the divergence of the two universes, which lead to the existence of two machines (or rather, two parallel sets of pieces) once the universes diverged from one another.