Honestly, River's mistake wasn't too bad. The reason he'd made it to begin with was because he intended on handing over the technique to the elves anyway. That, combined with how strict they were about adhering to rules, made River drop his guard.
He just hadn't anticipated how valuable the technique truly was. The elves, though, realized that. So while they did keep their word of conducting the investigation regarding the Sunborne family, they slowed things down so that they could observe the technique in practice as well. After all, testing it on one of their own was a lot riskier than watching someone else practice it, and study their progress.
Compared to what others would have done, the conduct of the elves was still respectable. But that wouldn't always be the case. After all, while these elves seemed honorable, any race was filled with good and bad people.
