Well, I doubt he is a serial killer in the making.
FAS is brain damage as I'm sure you discovered in your research. Many of my adult clients are FAS and although they have some serious challenges, I don't know of any that kill people.
FASD is a spectrum disorder, so there are varying degrees of seriousness. The first thing you need is a full evaluation and a good therapist that specializes in this disorder. Most cities have associations dedicated to FASD and that is a really great starting point. He is going to need a fair amount of intervention, and the earlier the better.
The two biggest things we see in FASD are very poor decision making ability and difficulty with self control. These folks tend to be very easily led and have many outbursts of anger. They do not have the same ability to control this as you or I. There are of course a lot of other issues, but again, it really depends on the severity. I encourage you to get involved in a support group and again, to contact a society or organization that deals with fasd. If you are in the US, here is a link to a good website that can help get you started in finding both resources for your child and for the family. I urge you to contact them and they can help you find additional resources in your area.
http://www.nofas.org/
I wish you well.