A possibility. The Patriots inflated the balls to the minimum amount of air, or slightly higher, and did it in a process where the ball were very warm (heated the air or the ball with the air in it) The psi would begin dropping slowly at room temperature, so the refs could have measured 12.5 and then 2 hours later they were down to 12, 11.5, etc and the rest of the difference is from being out in the cold. This would not be illegal.
If the Colts inflated to the max and had a .5 to 1.0 decrease in psi, those balls would be within guidelines.
There is a lot to be determined here and this is not cut and dried.
A few other questions:
1) Did the refs check the balls properly before the game (rumor is that they checked them at halftime with 2 different gauges so that is fishy)
2) Is the report of '2 lbs under' from halftime, or after the game? Did they reinflate at halftime (how many) and then they were -2 after the game?
3) I find it hard to believe every ball was -2 and there was no deviation. I think there is short-hand in that report, so what were the exact ranges?
4) Does -2 mean 10.5 (2 below the min) or 11.5 (2 below the max) or 11 (2 below the average)
5) Where and how were the balls stored during the game? The fact that all but one were deflated would lead to the conclusion that it was done by the guy holding the bag, since we probably only played with a few of them.
6) Is there film available of the sidelines that would show anything done to the balls?
7) What is the true impact of the weather
I'm sure there are others, but I'm not ready to jump to conclusions yet.
My final question is why did the NFL leak this information? They officially say they are not done with the investigation. If the measurements were at halftime why did it not get leaked for 2 days? Is the leak accurate? Are they trying to let the story out a little at a time to soften the negative blow, or to show their hands before interviewing the Patriots personnel? Whatever the reason it was clearly either done on purpose or is not 100% reliable information to begin with.