The rear ender is guilty by default in the absense of other information. You can always prove otherwise if you have the evidince. Preventing other people from

The rear ender is guilty by default in the absense of other information. You can always prove otherwise if you have the evidince. Preventing other people from gaming this default to your detriment is arguably the main point of dashcams. In ye olden days before 1080p everywhere it was considered somewhat common courtesy to hang around and make a statement to the police if you witnessed a rear ending that was undeniably the fault of the party who got rear ended.