[SPOILERS FOR FLASH SEASON 1,2 & POTENTIAL SPOILERS FOR UPCOMING EPISODES]
Lets start with ZOOM or Jay Garrick the man who had a great plan to take Barry's speed as he is dying but how could he know there was a speedster on earth 1 and other info about his friends -of course it wasn't random- except with some information from the man in the mask or should i say ................................
EDDIE THAWNE EARTH 1
OK, this could be strange but let's remember what happened in the season 1 finale exactly when Barry returned from time travelling, prevented reverse flash from returning home, Eddie shot himself and Eobard Thawne vanished from existence and the singularity opened again. Here comes the surprise........
Eddie's body was absorbed by the singularity.
Of course you remember that the helmet of flash Earth 2 transferred through the singularity from earth 2 to earth 1 & the singularity of course can do vise versa.
So what if Eddie didn't die at this moment, traveled to earth 2 where Hunter Zolomon found him and knew everything about the flash and his friends and kept him as a last card to guarantee his safety if anything went wrong with his grand plan.
We will find soon in the season finale.