Video captured from a rooftop camera in Japan appears to show North Korea's Hwasong-14 ICBM reentering the atmosphere, then breaking up and destroying the reentry vehicle.

A former United Nations missile inspector said Monday that North Korea's intercontinental ballistic missile reentry vehicle "did not survive" last week's test, meaning the hermit regime needs more tests.

Intercontinental ballistic missile (ICBM) Hwasong-14 is pictured during its second test-fire in this undated picture provided by KCNA in Pyongyang on July 29, 2017.

"You see small bright radiant objects that are shedding off the reentry vehicle — and then it suddenly begins to turn very dim," Michael Elleman, a 38 North think-tank analyst and consulting senior fellow for missile defense at the International Institute for Strategic Studies, told reporters in a conference call Monday. "That should not occur. Most likely it broke up into pieces."

On Friday, North Korea test-fired its Hwasong-14 missile, which flew about 45 minutes and splashed down off the northern coast of Japan. A rooftop camera operated by Japan's public broadcaster, NHK, appeared to have captured the missile's descent back to earth — and it shows what Elleman said is convincing proof of the reentry failure.

Pyongyang's first known launch of the long-range ballistic missile took place on July 4, but it's still unclear if that test survived the reentry phase. However, the Friday launch led to video of a critical stage of an ICBM missile's return to earth when the heat and stress on the weapon would be the greatest.

"In short, a reasonable conclusion based on the video evidence is that the Hwasong-14 reentry vehicle did not survive during hits second test," Elleman wrote on 38 North blog Monday. "If this assessment accurately reflects reality, North Korea's engineers have yet to master reentry technologies and more work remains before Kim Jong Un has an ICBM capable of striking the American mainland."

Similarly, Elleman said that if a nuclear device had been on the missile, then it probably wouldn't have survived the full journey. Elleman's past experience includes serving as a United Nations commission weapons inspector in Iraq, and a scientist at U.S. defense contractor Lockheed Martin as well as government services giant Booz Allen Hamilton in programs working with the Pentagon, among others.

"If the bomb itself were exposed to these very severe conditions, it would be torn apart," said Elleman. "In short, if the reentry vehicle breaks up, the bomb is not going to be useful — and it's not going to detonate."

That said, if the North Koreans have trouble making a survivable warhead they could still detonate the device at around 10 km altitude (or about 6.2 miles), Elleman speculated. "It would lose a lot of its effectiveness but that's an option. But I don't think that's what they would ultimately want their nuclear-armed missile to do."

On Friday, physicist David Wright of the Union of Concerned Scientists estimated that half, if not most, of the continental U.S. was within range of the North's Hwasong-14 ICBM missile. However, he said at the time it wasn't clear if the North Koreans reduced the weight of the payload from the Friday test to give it a longer range than the earlier ICBM test on July 4.

Another way to reduce the weight is to use lighter materials — perhaps on portions of the reentry vehicle. Having a perceived longer range on the missile (even if it can't support a weapon's reentry) could be something desired by the regime for sheer propaganda value.

Indeed, Elleman said he can't rule out that the reentry vehicle broke up because the North Koreans may have used lighter materials or a design to maximize the range.

Elleman said if the North took out key structural elements as well as some of the reentry vehicle's heat shielding, that would make that reentry vehicle lighter and "could certainly play a very dramatic role in causing this one to fail."

"My guess is they need to do another handful of tests [on the ICBM]," said Elleman. Nonetheless, he said, "An early deployment next year is possible."