Lynching was probably ok for small communities who would have made up most of a jury anyway, but in this case it would deny the whole world the opportunity to see justice done.
Besides, who knows what intel these guys have that would be given up in trade for a life sentence?
Yes, they are traitors and deserve to die horrible deaths, but do you really think it was all their idea? If they give up the other links, and those deeper in the web are brought to justice, then I'm ok with that to settle this for another 1000 years.