When North Korea launched its first intercontinental ballistic missile in the early-morning hours of 4 July, US military and intelligence personnel watched for a full 70 minutes, a source told The Diplomat's Ankit Panda.

During that time, North Korean leader Kim Jong-un smoked cigarettes and strolled around the launchpad under the US's gaze.

The US knew North Korea was in the final stages of building an ICBM after a recent rocket-engine test. The US knew North Korea liked to test missiles on the American Independence Day to send a message. The US knew this missile was different from any it had seen before, and the US knew it could destroy it with a variety of precision-fire platforms in the region. Importantly, the US also had Kim in its crosshairs for over an hour — and did nothing.

Those facts speak volumes about the security climate in the Koreas.

While it's “fairly standard that the US didn't strike the missile ahead of the launch,” Rodger Baker, the lead analyst of Asia Pacific and South Asia at Stratfor, a geopolitical consulting firm, told Business Insider, “the unusual aspect may be saying they were watching, or at least allowing that to leak.”

Video of the launch clearly shows Kim on-site, sometimes feet away from the missile. The next day, the US and South Korea put on a blistering display of precision-guided firepower demonstrating they could have both killed Kim and stopped the launch. But they didn’t.

By letting North Korea know it watched Kim as he prepared for one of his country's most provocative missile tests ever, Baker says, the US may have sent two powerful messages.

The decision fit with Secretary of State Rex Tillerson's statement that the US wanted “to bring Kim Jong-un to his senses, not his knees” and that regime change was not the US's ultimate goal.

But regime security is the reason North Korea wants long-range nuclear weapons in the first place.

If the US demonstrates it's not intent on killing Kim, that could communicate that there's “no need to continue” the missile programme, according to Baker.

But “if the program is continued,” Baker said, the US showed it could “strike it and Kim.” Though North Korea varies and tries to hide its launch points, the US tracks them vigorously, and footage of the launches always shows Kim nearby.

Perhaps rather than kill Kim and trigger a North Korean response, which could be massive, the US elected to signal that the best path to regime security would be to stay indoors and not play around near dangerous rocket engines, which have a habit of blowing up.