OK, time for some "Twilight Zone" music here. Whether he's the same guy or not, you have to admit that one great place for a serial killer is in the woods with a deer rifle.
If the authorities have spent shell casings from the 2001 homicide, it may not be that hard to prove. Every gun leaves it's own unique firing pin impression on a casing. When the police searched Vang's house they may have found other weapons. They just have to test those weapons to see if they get a match an wala, you have your killer.