When Cooper finishes his investigation at the Roadhouse, he has Ed come there, along with Leo. Then he realized that the waiter, and possibly Briggs, were missing. This might not make any impact, though, so look at it as an interpretation, connecting these three people to the Giant's three clues.

1. Big Ed: at the hospital, Cooper and company saw Ed outside Nadine's room and decided to stick around and listen to what had happened. That is when Cooper noticed the smiling bag in the bathroom. If they hadn't seen Ed out there, they would have probably missed this clue.

2. Briggs: I think this one is the most obvious. Briggs brought Cooper the owl transmissions and Cooper somehow deduced that Briggs was missing from this fateful reunion. Of course, the Giant brought him there, possibly because he saw Cooper come to a moment of realization earlier during the warm milk scene.

3. Leo: Maybe a bit far-fetched, but we were never told explicitly what the significance with boots was. Leo bought the boots from the Phillip Gerard, who is the basis for the third clue. Cooper put two things together and deduced that Leo had to be there.

And that's it. The Giant saw that Cooper had compiled everything that was needed and gave him the ring, which represents the investigation coming full-circle. He also said the magic phrase about the gum, which triggered Cooper's memory.

Thoughts?

best explaination I've heard, but will still remain the first stumble of hokiness to me in the series.

I think this was still a means of confusing and not letting info leak out of who the murderer is to the filming crew and public.  Ed was used as a script decoy, and in the script for this scene, Ben is arrested and then dies in place of Leland. 

Probably used these guys (Bobby, Ed, Leo, Leland, Ben) because they were being preventative.  Wonder if they shot any other characters being arrested. 

Adherence to the trappings of formality and tradition drives Cooper's mojo.

Known Facts: The bootprints made by Hank when he shot Waldo were the same brand as those sold by the OAM. The OAM was had formerly traveled in pharmaceuticals for an East Coast drug company. Hank and Leo were distributing illegal drugs to the local high school elite. Leo was receiving shoes from the same presumably East Coast company that OAM worked for, one of which now had a hollow heel. That is where Leo hid the incriminating Ben Horne tape.

Speculation: Did the hollow-heeled shoes arrive empty? Was there a former contact of the OAM's drug-company who worked as the middleman, picked up the shoes, created the cavities, filled them with an illicit substance, and mailed them off to Leo's aliases for him to drop into post offices along his truck route and pick up. A series of post office boxes are all that Leo would need. Nudge Nudge, Wink Wink, I don't want the old lady to know that I'm sending off photos to Fleshworld. A buyer returning unhappy purchases could be used as a cover for shipping payments back to the middleman. Perhaps the middleman was the guy from the Fleshworld ad who wore lingerie but his beard spoiled the effect, at least in Agent Cooper's opinion.