Washington (CNN) -- If the threat of underwear bombs became known last Christmas, why did airport screeners only recently begin aggressively checking for them?

The answer is two-fold, Transportation Security Administration Director John Pistole told reporters Tuesday. First, the lack of a permanent leader at the TSA hindered change, he said. Secondly, the agency needed time to train screeners on the new pat-down protocols.

The threat of hidden bombs became instantly clear on December 25, 2009, Pistole said, when authorities arrested Umar Farouk AbdulMutallab, a Nigerian man, after his failed attempt to ignite his hidden explosive on a flight from Amsterdam to Detroit, Michigan. TSA officials immediately started looking at what they needed to do to modify technology or pat downs to detect the bombs, he said.

But at that time, the top job at TSA was filled by a career official. The White House delayed nominating a TSA chief and then White House and Congressional Republicans feuded for a year over nominees. Much of the debate centered on whether the nominees supported unionization of airport screeners. Two of President Obama's nominees withdrew from consideration.

"Frankly it just came down to the fact there was not a presidentially appointed, Senate-confirmed administrator in place until I was confirmed at the end of June to make a really significant decision like that, that would have impact on a number of people," Pistole said. "That was a big part of it."

Pistole was sworn in as administrator in July and soon thereafter made the decision to go through "enhanced pat downs." Training time accounts for the rest of the delay, as the TSA quietly began pilot programs in Boston, Massachusetts, and Las Vegas, Nevada, in August, and rolled the program out nationwide in early November.

Pistole consistently has said it was his decision to implement enhanced pat downs. He said he opted not to publicize them in advance because he felt to do so would be to give a "roadmap" to would-be terrorists.

Implementation of the pat downs was further delayed because time was needed to train screeners on the new protocols, he said.

Those protocols are considered sensitive security information, and have not been shared with the public.

But Pistole said protocols do not allow for screeners to grope passengers.

Pistole said some passenger descriptions of the procedures are "so wildly outside the standard operating protocols that it just absolutely should not be happening. If it is, then we'll take appropriate action."

"If we receive any complaints from a passenger about something happening, then we immediately follow up both with that passenger and with our security officers," he said.

Most airport checkpoints have closed circuit television systems, which help investigators find out what happened, he said.

Videotape helped dispel one passenger's complaint that she was handcuffed to a chair and mistreated, he said.

"If there's a security officer that did something that's not appropriate, then we take appropriate action. I just want to make sure that I have all the facts," Pistole said.