As for the DNA thing, the only bit that is confusing is when they killed him. Some say earlier this week, Obama said it happened yesterday. A DNA test for a civilian usually takes 5-10 days (but you have to count in processing and etc. so the time is super inflated by artificial measures), that being said though, the fastest I've heard a DNA test being completed in was 48 hours. I wish I knew how long the actual test itself took though, because more than likely all you would need to do is add an hour or two to it and that was probably the most accurate assessment of how long the test actually took.
They got the DNA from his sister who died in an american hospital of cancer. A lot of people said the government extracted her brain or some other bollucks, which is just fucking weird. All they probably did was issue a subpoena and collect some blood and tissue samples. What's interesting though is that it was his half sister (hearsay is his dad has around fifty children with a score of different women, Osama was the only child from this particular mother). That really doesn't make much of a difference when it comes to autosomal testing though.