This part is confusing.
There was no incentive to move the 'taser'. At that point it was part of a crime scene. And if there was a tussles where the suspect had his hands on the taser, it would have potentially left fingerprints. By the officer moving the taser, he puts his fingerprints on them last, potentially covering up any evidence to the support. Or if he was going to move it, he simply could have used a handkerchief or similar cover to support his defense which would not have contaminated the taser surface.
All and all a odd part of the entire chain of events in total.
I have no idea why he appeared to move the taser. Others have raised the possibility that Officers are required to keep control of their weapons, and that Officer Slager knew others were in the area and might have tried to snatch it.
I do not know how much these tasers cost (reported to be 1,000$ each), so he might have gotten in trouble for not regaining possession of it. Why he dropped it on the ground near Scott, and then picked it back up is unclear to me.
Someone else at the Treehouse wondered if Slager might have retrieved it because of the potential for damage by incoming police cars running over it.
Since I have no knowledge of police procedures, I see this as an opportunity for learning, and will be closely following what develops over at the Treehouse. I followed them during the Zimmerman and Brown mess of bad reporting, and found them honest, unbiased, and accurate.