I voted unsure. I believe that he fits the profile of a serial killer and that his motive is the same, but these murders could have been his first, which would mean that he did not yet meet the criteria for being a serial killer at the time the murders were committed.
I think that seeing the video of himself captured by Libby scared him straight temporarily, and I don't know whether he has started killing again. If he's one of the people who has been interviewed by law enforcement, then I think that he has probably remained dormant. Serial killers can control themselves, in my opinion, and are likely to stop killing after being interviewed by police. Once they know that law enforcement is looking at them, the risk outweighs the reward because they have a strong sense of self preservation.
If he has managed to fly completely under the radar, then he very well may have killed again, but if he has done so, I think that he has made a point of changing his M.O. in order to avoid capture.