He's messing with some wires.
Also, he's got a right-hand holstered handgun.
If you are interested in seeing more opinions and analysis of the shooting, please check out this Patriot’s blog:
http://freenorthcarolina.blogspot.com/2016/01/finicum-zoomed-in-at-50-speed-and-can.html
http://freenorthcarolina.blogspot.com/2016/01/lavoy-points-out-person-that-takes.html
http://freenorthcarolina.blogspot.com/2016/01/the-ambush-and-murder-of-robert-lavoy.html