When North Korean engineers launched a satellite into space December 12, it seemed like business as usual, with the familiar cycle of condemnations from the West and statements of defiance from the Hermit Kingdom. But that launch also led many U.S. intelligence analysts to assess that Pyongyang possessed the ability to miniaturize the components necessary to yield a nuclear explosion for a crude warhead that would sit atop a ballistic missile.

After the North Korean launch, U.S. Navy ships managed to recover the front section of the rocket used in it, according to three U.S. officials who work closely on North Korean proliferation. That part of the rocket in turn provided useful clues about North Korean warhead design, should the next payload be a warhead rather than a satellite.

The same basic engineering and science needed to launch a satellite into space is also used in the multistage rockets known as intercontinental ballistic missiles. The front of the satellite rocket, according to three U.S. officials who work closely on North Korean proliferation, gave tangible proof that North Korea was building the missile’s cone at dimensions for a nuclear warhead, durable enough to be placed on a long-range missile that could reenter the earth’s atmosphere from space.

“Having access to the missile front was a critical insight we had not had before,” one U.S. nonproliferation official tells The Daily Beast. “I have seen a lot of drawings, but we had not seen the piece of that missile at that time.” This official continues: “We looked at the wreckage from the launc,h and we put it together with other kinds of intelligence and came to this judgment that they had figured out the warhead piece.”

The Defense Intelligence Agency (DIA) released a classified assessment last month saying that it now has “moderate confidence” that the “North currently has nuclear weapons capable of delivery by ballistic missiles however the reliability will be low,” South Korea has provided additional intelligence bolstering this conclusion, according to U.S. officials.

That assessment, in line with, but more assertive than earlier comments from the agency, was made public three days ago in a question from Rep. Doug Lamborn, a Republican from Colorado, to the chairman of the joint chiefs of staff, Gen. Martin Dempsey. Pentagon spokesman George Little and the director of national intelligence, James Clapper, soon after the disclosure issued statements trying to play down the news. Clapper said, “It would be inaccurate to suggest that the North Korean regime has fully developed and tested the kinds of nuclear weapons referenced in the passage.” He added, “North Korea has not yet demonstrated the full range of capabilities necessary for a nuclear armed missile.”

But neither Little nor Clapper disputed the basic judgment that North Korea could likely build a nuclear warhead of low reliability. While the DIA assessment does not represent the view of all 16 U.S. intelligence agencies, the recovered satellite rocket helped move CIA analysts away from their skepticism about North Korea’s ability to build a nuclear warhead as well. “The DIA was always more forward leaning on this,” one U.S. official said. “The CIA was always extremely cautious on this. The doubters in the CIA finally found some common ground with DIA when we did the recovery.” (The CIA declined to comment.)

Intelligence suggesting North Korea could design a nuclear warhead has been building for many years. A.Q. Khan, the man considered to be the father of the Pakistani nuclear program, for example, has said in interviews and correspondence that in 1999 on a visit to North Korea, he was shown boxes of components for three finished nuclear warheads that could be assembled within an hour.

One U.S. official who works on North Korean proliferation said there was reason to believe that Khan could have been lying when he said this. “Khan was like a used-car salesman,” he said. “He wanted future customers to think he could get them the full package even though many times the equipment would not work as well as he said.” This official said there may have been components for warheads in a box, but “we never knew if those components could actually work.”

More recently, though, other kinds of intelligence have also come to the attention of the U.S. intelligence community that suggest North Korea has mastered the miniaturization and warhead design work as well. Another U.S. official who works on North Korea work told The Daily Beast that South Korea has recently shared more traditional kinds of intelligence with the United States about North Korea’s warhead design work, but did not get into the details of that intelligence.