Lets take a look at some things here before we get into "investigate dolphins"
1. There is no rule in the NFL against what the dolphins are doing. There are things in place...job security, cap floor, trade deadlines, honest injury reports...that are in place to discourage "tanking", but there is no actual rule in the bylaws.
2. In recent years you have had the Browns, Colts, and Raiders all do some form of tanking. Browns hired Hue Jackson, the Raiders got rid of pro-bowl players, and Colts started Painter. The Dolphins are not doing anything different from what those other programs have done, just did it a lot cleaner and acquiring a ton of resources for a quick turn around.
3. The value the Dolphins have received from trading away two of the better young players is insane. No one could possibly look at those trades as anything other than great value for the phins and not some "firesale". From two players, the team received 3 firsts and a 2nd. For two players that have no accolades.
4. The Dolphins made legit attempts to acquire Clowney and Flowers during the off-season. It didn't work out but the team did go after those players.
5. Now, if the NFL is really going to go after the DOlphins, then they need to go after every single team that sits starters at the end of the season after they wrapped up a playoff spot. I mean, those teams are literally not putting out the best they can to win that game. Meaningless doesn't matter, if the NFL is going to come after the Phins, then that needs to be investigated as well. I'm not saying the NFL should, but just the ridiculousness of "investigating" the Dolphins, when this is allowed.
6. I saw Mortenson pu out a tweet about "protecting the shield" and in NFL that employs child abusers, wife beaters, rapists...they are concerned with a team being undermanned? This is a league that not only employees Rothlisburger and Winston but celebrates them, but the Dolphins are the ones hurting the image of the league?