Rear collision who's at fault?

Driving my sisters to go get dinner I'm following a car about 20 yards behind. The car starts tapping their brakes on a green light for no reason so I slow down but the space between us slowly closes, and then the car slams on their brakes as soon as the light turns yellow. Their car being a newer model stops on a dime while my older 2000 ford kicks on abs and slams right into the rear end. Later when we both pull over, it Turns out the car driver was a friend of my sister and recognized my truck which explains why she was hitting her brakes before. But who is at fault. I know typically rear ends are the back cars fault but if the forward car was already hitting their brakes for no reason and then slams on their brakes to avoid going through a newly turned yellow light leaving me no room to stop or move lanes because the car behind me in the other lane went through the yellow with plenty of time to avoid running a red light. Who is really at fault?

It's all yours, buddy. You are supposed to follow at such a speed and distance that if anything unexpected happens you CAN stop in time. The often used example is of a child running out into the road in front of the car ahead, when the driver will of course brake hard and you should be able to stop too.

Its your fault. You failed to stop in time.

How are you going to prove what you claim? If the other driver won't admit to causing the accident and if you have no witnesses, you are screwed.

Take it to Court as long as your witness will testify as to that what happened!

She is you should never tap your breaks when someone you know is following you that person was being an ***

No matter the reason or how it happened the person that strikes the rear of a vehicle is at fault.

It does not matter why she tapped her brakes. She could have a bee in the cab or been scared by something. You saw the lights so could have and should have slowed enough. Or you were following too close to begin with. You would only have an excuse if her brake lights did not work. If they were smashed in the accident, you could claim they did not work?

100% your fault, Jacob. You failed to maintain a proper and safe distance to avoid a collision in such a situation. You even had indication from the other driver by them " tapping their brakes" and you still failed to leave enough area to avoid a collision.