Something people seem to fail to realize. The gun makes a bang when it's fired(obviously) but, the projectile also makes it's own noise as it breaks the sound barrier through the air.

Here's a couple examples. https://www.youtube.com/watch?v=stzSY1gT0m0 https://www.youtube.com/watch?v=wSfoJkAq--k

Notice how similar it sounds to the alleged second shooter.. The only way to tell from this video is there is truly a second shooter is to count the muzzle reports and compare them with the other higher pitched "second shooter" to see if they match up noise for noise.