The Wikipedia plot summary has this bit near the end, emphasis mine:
Abercrombie informs Dixon that the DNA sample does not match DNA found on Angela's body and that the man was overseas on military duty and had come back to the country 9 months before. Dixon stays confused and does not connect the clues.
The clues of the whereabouts of the DNA guy 9 months ago. Dixon was not able to figue out the country the guy was in 9 months ago using the chief's clues. The chief couldn't just tell him that because it is classified information so he thought of implying it to Dixon using the following clues, respectively: