Who was "at-fault" in this traffic accident?

Vehicle #1 is going straight ahead on a public street. Veh. #1 turns on her left turn signal to enter the middle turning lane, in order to make a left turn ahead. Veh. #2, also going straight ahead, has just left private property and enters the middle turning lane, hitting Veh. #1 in the left side of her vehicle. both drivers claimed they had the right-a-way in the middle turning lane. in your opinion, who was at-fault?