Yep. Just as a nitpick (your remark is close enough to the process), the weight of evidence at indictment is not beyond a reasonable doubt. Prosecutorial ethics (see Nifong) is that the case should not be tried unless the DA believes the facts will support a conviction (beyond a reasonable doubt), which can be read as either a more strict standard, or slightly looser standard. Generally, weight of evidence is for the petit jury to decide. The grand jury might consider evidence from an unreliable witness (taking it as reliable), and use that to justify the charge. It's ultimately up to the petit jury to decide if the witness is reliable or not; although testimony that is demonstrably false (see Nifong again) is not supposed to support charging.
Oh, one more thing. The presence of generalized bad blood between two gangs doesn't even support an accusation that any particular individual agreed with another, to rumble. It's utter absence of evidence, so the "weight" of it is a nonsense inquiry.