I am not condoning what Dekker's did but his attorney is correct, this is a matter for Iowa State and the NCAA. Under Iowa Code there is no law preventing him from placing the bets, the Iowa Code is specific to the gambling entity that they have to have controls in place to prevent such a thing from happening, but not the individual gambler themselves. I've posted the Iowa Code a few times in one of these threads.
Now the tampering with evidence is a no no, but can you really tamper with evidence of something that wasn't illegal?