Everyone is missing the crux of the problem/misunderstanding: Inequity (actual or conceived). Consider the same situation but reverse the races and many people think that the boys would have been arrested and interrogated. Instead, the DA obtained a search warrant based on probable cause that evidence of a crime was there. So it seems that the DA is giving lenient treatment to the boys.
If the police had PC to obtain a search warrant, why didnt they get one for arrest too? My best guess, they didnt think they had PC for an arrest because the victim could not identify anyone.
At this point, it seems without the DNA, the CA cannot meet the burden of beyond a reasonable doubt. Her claim is that essentially 24 guys conspired to let 3 other guys rape a person. That is an unplausible claim in itself, but add to that they did not leave a shred of forensic evidence, not so much as a white pubic hair, and you have reasonable doubt.