Over the course of the episode, we learn that Professor Kellerman was not the one to hit Brooke and Jamie on the bridge, but it was his son, Ian Kellerman.

Did Ian Kellerman drive the car?

So Ian Kellerman was the driver of the car that slammed into Jamie and the gang, shoving them off the bridge and into the river. This dude is obviously a jerk, and once Nathan puts two and two together, he will no doubt want to void that contract.

Who hit the car off the bridge OTH?

On the other side of the spectrum was the discovery that it really was Ian Kellerman who hit the car Brooke and Jamie were trapped in that scary, stormy night.