Kim Jong-nam, the slain half brother of North Korean leader Kim Jong-un, was an informant for the Central Intelligence Agency (CIA) who met on several occasions with agency operatives, Efe news quoted an informed source as saying here.

“There was a nexus” between the US spy agency and Kim Jong-nam, the source said on Monday.

Kim Jong-nam was killed in the Kuala Lumpur International Airport in Malaysia in February 2017, when two women smeared his face with the nerve agent VX. US and South Korean officials have blamed the attack on North Korea, which it denies.

Many details of Kim Jong-nam’s relationship with the CIA remain unclear. Several former US officials said the half brother, who had lived outside of North Korea for many years and had no known power base in Pyongyang, was unlikely to be able to provide details of the secretive country’s inner workings.

They also said Kim Jong-nam, who resided mainly in Macau, was almost certainly in contact with security services of other countries, particularly China’s.

The CIA has declined to comment on the development. Chinese officials didn’t respond to a request for comment.

The fact that the CIA held meetings with Kim Jong-nam illustrates the lengths US intelligence will go to gather information about the hermetic country.

There has been speculation among former US officials and analysts that outside countries, including China, saw Kim Jong-nam as a possible successor to Kim Jong-un should the latter’s rule be in danger.

But US intelligence agencies concluded that Kim Jong-nam was ill-suited to fill such a role, several former US officials said.

News of the CIA’s relationship with Kim Jong-nam comes as nuclear diplomacy between the US and North Korea is at a standstill following a February summit in Hanoi between Kim Jong-un and US President Donald Trump that ended without an agreement.

Kim Jong-nam’s role as a CIA informant is also described in a book about Kim Jong Un, “The Great Successor”, written by a Washington Post reporter and due to be published on Tuesday, according to news reports citing excerpts of the book.

Kim Jong-nam travelled to Malaysia in February 2017 to meet his CIA contact, although that may not have been the sole purpose of the trip, Efe news quoted the source as saying.

Police testified during the trial of the two women that Kim Jong-nam had spent several days on the resort island of Langkawi, where he met an unknown Korean-American man at a hotel.

Malaysia in May released from prison a Vietnamese woman, Doan Thi Huong, who was charged in Kim Jong-nam killing. Her co-defendant, Siti Aisyah from Indonesia, was freed in March.

After Kim Jong-nam’s murder, his son Kim Han-sol and other family members were spirited out of Macau by a group of North Korean dissidents known as Cheollima Civil Defense, the group told The Wall Street Journal. Kim Han-sol’s current location isn’t known.

Kim Jong-nam was Kim Jong-il’s eldest son, and for a while it appeared he was being groomed to succeed him. But he fell from favour in the early 2000s.