I was in accident were I was backing up. I was 75% backed up when I was hit in the parking lot. I was a stopped and could see the other car coming.

They didn't see me until collision. The speed limit in the parking lot is posted as 5 miles per hour, and they were going faster than that. The other car went over a speed bump less than 5 feet from my car.

They had a child in the car.

My questions,
How can I prove they were distracted?
Is there case law in Washington State regarding case law and backing up, parking lots and distracted drivers?

I truly believe the other driver is at fault despite I was in the process of backing up. The place of impact was my passenger side bumper which was pulled away from my truck.

Any help with establishing evidence, legal precedent and/or case law.

Thanks.