There may be no significance, but given how close to the murder scene it was found, the fact that it had been concealed and that it appeared to have been there a long time, I'd have thought they would have wanted to test it - after all, if it turns out to be the murder weapon, it may well have the killer's DNA on it.
If they're convinced they got the right person, finding the murder weapon with his DNA would prove their case conclusively. So what are they afraid of I wonder?