That's what I've seen since first analyzing the images.
Great sleuthing by the folks on here re: where on the bridge this guy waa. My first instinct was to say they were close to the end of the bridge when those images were taken from a trail cam, then I figured it must be phone video. I thought he was close to them, as in within 4 or so steps, but the quality of the images is poor enough to suggest he was at least 50 feet away.
I just grabbed a spare phone of mine, an HTC which is about a year old. Took a 3 second video in my backyard, which has trees and brush along the property line about 60 feet away, with a grassy pathway. Moved/panned the phone slightly for the 3 sec. video. Then came inside to take a screen shot to analyze it
Zooming in on stuff 60+ feet back reveals no depth of field, and other optical effects which photographers look for in image quality. Plus, this guy was moving.
I maintain those images were taken mere moments before he attacked them. He could have waited near the spot where they were murdered, waiting for (I hate to say this) the right victim or victims to get on the bridge. He watches them, notes the speed with which they were traveling across the bridge, and then figured he had to make his move. Walks along the creek on the far side, gets on to the bridge, and mere minutes later is almost across the bridge when the images were taken on the phone.
Almost across the bridge, and mere steps away from the girls, he pulls out one, maybe two weapons. They panic, and start running down the embankment towards the creek, then follow the creek while he's chasing them.
They get to the creek and start to cross it. He's taller, and is able to cross the creek just a little more quickly than them. Catches up either in the creek or on the far embankment, maybe it was in the creek the one girl put up a fight.
This scenario explains further the tight time frame. They could have been dead by 3PM, maybe even as early as 2:30 or so.