What's Up With Google's Search Timestamps?

Someone pointed this out to me, and after googling around, I could not figure it out. The issue seems to be that Google's timestamps are incorrect for search results,and as a software engineer, I find that somewhat surprising.

The Sandy Hook School shooting took place on 12/14/2012:

http://en.wikipedia.org/wiki/Sandy_Hook_Elementary_School_shooting

Now, if you go into Google and search "Sandy Hook School", then go to "Search Tools" and filter by

12/8/2012 - 12/3/2012 (5 days before the tragedy occured), you see articles about the shooting with timestamps up to 4 days before the shooting actually occured 12/10/12 (see image below). Why are google search stamps incorrect for this particular customized search?