What did the Forensics investigation of the Madeleine McCann's flat in Portugal turn up?

The Madeleine McCann investigation seems to rely almost entirely on eye witnesses, but police crimes are most often solved based on forensics. Do they have any DNA samples from the flat, fingerprints or footprints to go to help identify the kidnapper? If the crime scene was degraded then in what way was is degraded, why wasn't it cordoned off as a crime scene; did cleaners come in the next day and wipe all the evidence off? Will these be the kinds of leads the Metropolitan Police will follow up on based on Prime Minister Cameron's request?