Witness to an accident at Canada way and Edmonds?

Hi there. Not really sure how to word this post, or if I should go into detail ? but here we go. I drive a Kia forte (grey) I was headed eastbound on Edmonds st. going towards Canada way. There was traffic backed up in the middle lane, as I was approaching the left turn lane. There was no one in the left turn lane except right at the intersection, quite a ways from where I was. There was a black Mustang SUV in front of me, slowly creeping up to the car in front of them in the middle lane. I had my left turn signal on for quite a while, when I started to head into the left lane. All of a sudden I see the mustang in front of me swerve over into my lane and then at the same time slam on the brakes for no reason at all. I legit just came from getting my brakes done so they aren’t as sensitive as they were before. I tried braking but I couldn’t in time. I ended up rear ending the mustang. The woman got out smiling and laughing. Wouldn’t give me her license for about 10 mins, all while making phone calls to everyone except the police. I really need a witness in this case 😭

Is there anyone that saw this accident? Or have dashcam footage? I’m going to contact the businesses around and post some posters as well. Please let me know if you saw anything or have any footage!!! THANK YOU