National Geographic finds that some of the damage evident was inflicted by pressure or other means long after death, see http://ngm.nationalgeographic.com/ngm/0709/bog-bodies/bog-bodies-p2.html. Sometimes people even stepped with heavy clog on a body during the excavation process.
There are hundreds of such bodies: in Denmark, including Grauballe Man in Jutland; but also in Poland, Northern Germany and the Netherlands.
http://www.archaeology.org/online/features/bog/exhibit.html. Many cultures tossed items and bodies in bogs. Finding those reasonably intact is not evidence of human sacrifice, but of the conditions of tanning.
The display of the Tollund Man we saw at Silkeborg was responsibly non-committal in leaving numerous options open, but the visuals and suggestivity outweigh the technical non-conclusions, see http://www.tollundman.dk/doeden.asp; and http://www.pbs.org/wgbh/nova/ancient/tolland-man.html. But it is this very stress on needing reasons that is also of interest.
Tacitus, Roman historian, apparently referred to the manner of death as punishment for cowards, the unwarlike, and those who "disgraced their bodies". And that is the only contemporaneous report we have. See the Archeology reviews site, and http://www.usatoday.com/tech/science/columnist/vergano/2011-01-16-bog-bodies_N.htm.