1 You're assuming that rifle originally had a serial number. It wasn't all that long ago (I can't remember exactly, but I think sometime in the 1960s) that it first became a legal requirement for guns to have serial numbers. That .30-06 belonged to Kirk's killer's grandfather, and so pre-dates the need for serial numbers.

You'll notice that none of the articles -- the ones from reputable sources, anyhow -- say anything about serial numbers having been filed off. 

2 A good point Dana.

I am not saying this is so but it is worth paying some  attention anyway. It certainly would be like the mainstream media to not report that little detail.

This was a case of "we report, you decide".

3 Think back to all the instances you can remember where serial numbers have been filed off a recovered weapon (not just a firearm) suspected of being used to commit a crime. The media is all over it like a cheap suit.

In the case of this elderly .30-06 hunting rifle, I believe I've seen exactly one reference, and the verbiage was that there was no serial number, not that a number had been filed off. So the writer got it right. And the stories that didn't mention any serial number got it right too.

Amazing, once you think about it.

4 Fair enough.