(CNN) Deflategate is not just a bunch of hot air, the NFL said Friday.
The league said the Super Bowl-bound New England Patriots used footballs that didn't meet league specifications in the first half of the AFC championship game last Sunday.
"While the evidence thus far supports the conclusion that footballs that were under-inflated were used by the Patriots in the first half, the footballs were properly inflated for the second half and confirmed at the conclusion of the game to have remained properly inflated," the NFL's statement said.
The statement said the NFL wants to know "specifically whether any noncompliance was the result of deliberate action. We have not made any judgments on these points and will not do so until we have concluded our investigation and considered all of the relevant evidence."
Forty interviews have been conducted, the NFL said, but it didn't say whether investigators had talked to star quarterback Tom Brady or coach Bill Belichick.
Brady, the central figure in the controversy, said Thursday that nobody from the NFL had talked to him. He and the coach said they don't know how the balls became under-inflated.
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Patriots Chairman and CEO Robert Kraft said the NFL spent three days talking to Patriots employees, but he didn't specify whether Brady or Belichick were interviewed.
"During the three days they were here, we provided access to every full- and part-time employee the league's representatives requested to speak with and produced every communication device that they requested to search," Kraft said in a statement, his first about the the flap dubbed Deflategate.
Eleven of the 12 game balls the Patriots provided were under-inflated by about 2 pounds per square inch each, ESPN reported. Regulation pressure is 12.5-13.5 psi. A ball with lower inflation is supposedly easier to grip and may give the passer a competitive advantage.
NFL Executive Vice President Jeff Pash and Ted Wells of the law firm Paul, Weiss are leading the investigation, the statement said, and Renaissance Associates, an investigatory firm, has been hired to assist in reviewing electronic and video information.
The investigation started "promptly on Sunday night," the statement said, " and so far has included 40 interviews with "Patriots personnel, game officials, and third parties with relevant information and expertise."
The inquiry started after Indianapolis Colts linebacker D'Qwell Jackson intercepted a Brady pass in the first half. The Patriots beat the Colts 45-7.
According to Newsday, he took the ball to his team's equipment staff, which then informed head coach Chuck Pagano, who told general manager Ryan Grigson, who told NFL director of football operations Mike Kensil, who told the officials on the field.
However, on Thursday at Pro Bowl practice, Jackson said he didn't say he thought the ball was flat.
"I made a great play on a great player, and I wanted to keep it as a souvenir," Jackson said in an interview with CNN affiliate KNXV. "So I handed it off.
"The next thing I know I'm in the middle of Deflategate, so I don't know how that happened, and I was just doing my job, and I seem to be in the middle of everything. But I've got a ton of respect for that organization, New England. They outright beat us hands down and that's pretty much all I can say about it."
The Patriots will face the Seattle Seahawks in Super Bowl XLIX on February 1 in Phoenix, Arizona.
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