My impression is that the police began interviewing the circle of friends for the boys from downstairs, after Stefan Bonassi mentioned on 11/3 that a guest (Rudy) had fallen asleep on a toilet and left an unflushed turd therein.
Based on the similarity to the unflushed turd upstairs, they began interviewing the circle of friends, which led them eventually to Rudy by name. They then checked Rudy's immigration record for his palm print, and sent it to Rome for an expert's view, and were able to match it to the bloody palm print from the crime scene.
That's what I recall, others may know more.
I agree, that likely it was good old fashioned police work which eventually had identified Guede as their suspect.
After all, based upon finding African hairs in Meredith's bedroom, there weren't that many sub-Saharan African men in Perugia, so once DNA had cleared Lumumba, that put the focus onto the African guy (Guede) who had visited the boys downstairs on an occasion or two.
I doubt if Guede's immigration paperwork had his palm-print. Fingerprints, yes, but not likely a palm-print, and I doubt if the bloody palm-print left on Meredith's pillow was very clear.
The Italians likely didn't have a CODIS type of DNA database back in 2007.
Since the boys downstairs obviously didn't know Guede's actual name, only that he often played basketball at the nearby court, that could have been their main lead.
The police may have found several photographs of African immigrants in their immigration database, and perhaps they had a picture of Guede in there? Or, perhaps they had a clear picture of Guede's face taken the night of the murder on the garage's CCTV system?
With pictures of possible African suspects in hand, the police could have then gone to the basketball courts and found someone there who knew Guede's name? Even without suspect pictures, the police could have merely asked people at the court if they knew an African guy who played there, and got lucky?
If Guede did have a police record as that UK article had reported, then that may have helped. Even if Guede didn't have an actual police record, it appears that many police officers were aware of Guede. Once it became clear they were looking for an African suspect, perhaps an officer who had dealt with Guede in the past mentioned Guede to the investigators?
One way or the other, once they had Guede's name, they went to Guede's apartment and used his toothbrush to obtain his DNA sample, and BINGO, they had their match.
While it's all conjecture how they eventually found out Guede's actual name, I seriously doubt if Guede's palm-print was on file in his immigration papers.
BTW - as for using DNA to clear Lumumba (and later they used to match with Guede), what DNA sample found in Meredith's room were they using for that? Touch DNA on Meredith's bra or purse?
Touch DNA is generally LCN-DNA, and back in 2007 Stefanoni's lab didn't even seem to have the right equipment necessary for doing that.
Likely, the perp's DNA they found at the crime scene was either from the semen sample, or the vaginal swab, or from some of the blood that had surely dripped from Guede's cut fingers.
I.e., in Meredith's bedroom they obviously had found an ample sample of the perp's DNA that normal DNA testing could be used to identify as belonging to Guede (and to exclude Raffaele and Lumumba).
