One of the only Westerners in the world to visit North Korea's primary nuclear plant has lifted the lid on conditions inside.
The regime has fired up a reactor capable of producing weapons-grade materials at Yongbyon Nuclear Scientific Research Center, satellite images revealed this week.
Secretive leader Kim Jong-un had expelled the the International Atomic Energy Agency, which made the "deeply troubling" revelation, from the site in back 2009.
And though the site was already outdated when inspectors last visited, those who have been inside warn that its bomb-making abilities are not to be underestimated.
Joel Wit, who works with the 38 North watchdog, was allowed to visit in 2008 when the regime was persuaded to denuclearise by the US.
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He said: "I always had the feeling it was like an old Soviet nuclear installation.
"There were some very large buildings there and it's clear they represented a lot of work and a lot of money, but it wasn't up-to-date, modern technology.
"It wasn't even close to up-to-date technology, I mean the welding was not well done and clearly the equipment was old - so it wasn't modern at all.
"But there were plenty of places like that in the Soviet Union too and they all worked - so that was the bottom line."
He added: "Even if those steps [to denuclearise] had been completed, they still could have restarted it. They weren't irreversible.
"I suspect that they could have just restarted the reactor and continued producing fissile material the way they had been producing it before."
Once activated, he added, the reactor would "of course" have good capacity to produce weapons-grade nuclear materials.
It was the reason the US tried to convince North Korea to denuclearise with its Agreed Framework in 1994, he said.
"We knew what was going on there," he said.
"We had our own estimates of how much plutonium they would have been able to produce if the programme continued to move forward the way it looked like it was moving forward.
"They would have been able to produce a lot of plutonium there."
Mr Wit made his comments in an interview with Pen News in 2018.
Keith Luse, the executive director of The National Committee on North Korea in Washington DC, accompanied Mr Wit during his 2008 visit to Yongbyon and photographed the site.
Also speaking in 2018, he echoed his colleague's concerns.
"It has the potential to be an effective facility to manufacture fissile material," he said.
Yongbyon's construction began in 1961 and in the decades since it's become a regular bargaining chip in North Korea's nuclear negotiations with the outside world.
In June 2008, the regime even destroyed the cooling tower at the plant, blowing it up in front of an audience of international journalists and diplomats.
In 2019, Kim Jong-un reportedly offered to further dismantle the plant during his second summit with then-president Donald Trump, asking for sanctions relief in exchange.
His offer was rejected, however, and it's unclear if the facility has ever been fully disabled.
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