It's the type of test. If you have a suspect and you have DNA evidence you can do a quick test that is fairly accurate to include or exclude that suspect. If it excludes the suspect, the exclusion is 99% accurate, if it includes you have to do further testing for the same accuracy which can take up to 3 weeks. Now if you have DNA and no suspect to compare it to, then it's a bit of a longer process. The quick DNA tests are great for comparison and can quickly identify a suspect who matches so that they can be held and charged, but they still have to do further testing for accuracy purposes. Remember too, this area is large, there's going to be a lot of DNA, some from people who were helping with the search, some are kids out drinking in the area, other hikers, etc. So they need to rule out those who aren't potential suspects.