Could there be a third killer at the time of the Woodsboro murders? Evidence suggest's possibly.
1) Sidney is attacked in the bathroom by Ghostface who fails to kill her, then goes on to kill Himbry. Stu is outside and I'm sure people would notice if Billy went missing for even a second.
2) When Tatum and Sid are done talking, they walk off and we see Ghostface watching them in the bushes, in the very next scene Billy and Stu are in the video store, it would be impossible for either one of them to get back to the store that quick.
3) In conjunction with 2, Ghostface is also following Sid and Tatum around in the supermarket.
Could there be a third killer or is it just a plot hole? Could the third killer be Roman?