The official has knowledge of the case and spoke on condition of anonymity because the investigation is ongoing. The official said there was no forensic evidence against the men.
Officials expect the case to be filed with prosecutors by Monday.
The arrest of the men Thursday was a dramatic development in the case because police had already nabbed another man, Giovanni Ramirez, as the main suspect. He remains in custody for a parole violation.
Forty-two-year-old Bryan Stow was nearly beaten to death by two men after attending the March 31 home opener between the Giants and Dodgers.