*Spoilers*
The movie didn't explain anything, it sets up the premise of the reoccurring day. Then it establishes that the ending of every day for the main character is death by cop. It then just starts to break logic, with a drug raid and armed robbery which don't seem to exist in any other time lines but the ones they appear in. Finally they end up explain that the cop is also time travelling but then this plot point is never addressed. For someone who likes the premise but wants a complete movie I'd suggest Palm springs and if you want the exploration of the black death by cop angle check out See you Yesterday.