So, I've got a theory (that I'm putting in a separate post since the last post is already pretty big): We're going to find out that he was using SkyBonus awards regularly as part of his travel agency's business model, effectively commercially selling SkyBonus awards. If he was doing that in such a way as to undercut Delta's pricing (particularly on one-way international trips with nosebleed sticker prices), I can see a problem for Delta. That's also the only way I can see him actually using 42m SkyBonus points in a reasonable timeframe (since if the points were mostly expiring unused, the allegations of harm from fraud would seem to be rather stretched..."Man racks up 42m SkyMiles" is a headline; "Travel agent who drove $7m in business to Delta and hacked a back door to get a free trip to Hawaii" would seem to be as likely to get a complaint from the jury about why they're even in the courtroom as it would to get a conviction).
If this was concentrated on a few routes, Delta could make a more sensible claim that his actions were suppressing overall ticket prices due to the scale of the action and the pax ultimately paying him less for a ticket than they would have paid Delta. Basically, it isn't "just" that he was pocketing a bunch of miles; he was actually making a hash of their yield management system in a few places.