I really think we need to ask ourselves how LE could possibly know the killer only walked 5 feet into the house without any evidence except the shell casings.
IMO, the answer is that it is not possible. The only way they would be able to state with certainty that the killer only went 5 feet into the house would be either an eyewitness other than JC directly observing the killer commit the crimes (IMO, we can almost certainly rule that out) OR as a result of some type of forensic evidence that they collected.
So, logically, either:
1) LE lied about knowing the killer only went 5 feet into the house
2) LE lied about not having any evidence aside from shell casings
3) They have an eyewitness (IMO, extremely unlikely to the 9th degree) or
4) The DM completely misquoted LE.
Those are the possibilities I came up with...can anyone think of any others?