Just to expand a little, now I've had a think.
In this case the skeletons were clearly not recent and were found on a known archaeological site. The way they were lying, plus whatever was found around them (the context) suggests a legitimate burial.
If the skeleton had been much more recent than they were expecting, or if the site hadn't expected to contain them, then investigations would be stepped up. Obviously, if the condition of the body suggests a two-hundred or two-thousand year old murder, the police aren't going to be able to do very much about it, and they'll usually bow to an archaeologist's expert knowledge.
This link looks quite interesting:
http://www.spoilheap.co.uk/digbone.htm