Seoul (CNN) It was her first assignment as a North Korean secret agent.

In 1987, Kim Hyon Hui put a bomb on board Korean Air Lines Flight 858, killing all 115 on board on what she says was the direct order of Kim Jong Il, the son of North Korea's then-leader Kim Il Sung.

"The mission was to block the upcoming 1988 Seoul Olympic Games," says the soft-spoken 55-year-old, who in 1990 received a presidential pardon for her role in the atrocity after standing trial in South Korea.

Her dramatic story shows the lengths Pyongyang was prepared to go to disrupt the 1988 Summer Olympics, which were seen as a showcase for the South's development. The Boeing 707 blew up on November 29, 1987, over the Andaman Sea off the coast of Myanmar.

Three decades on, the situation couldn't be more different -- North and South Korea will walk under a joint flag at the Winter Olympics that kick off next month in the South Korean city of Pyeongchang, and athletes from both sides will compete on the same hockey team.

However, Kim warns that North Korea hasn't changed since she worked as a spy for the regime, and Pyongyang has still not apologized for the bombing or accepted responsibility.

"They are using South Korea to overcome their difficulties ... to achieve their goal they execute their own people, siblings, families, do not be fooled, North Korea has not changed at all," she says.

Wreckage arrives at Gimpo Airport in South Korea for investigation on May 22, 1990

Training

We met Kim in a nondescript hotel room in South Korea, where she was accompanied by half a dozen bodyguards.

We can't disclose the location as she and the South Korean government fear North Korean agents may still be trying to silence her.

With good reason -- Kim trained for more than seven years to become a secret agent and has intimate knowledge of North Korea's security operations.

Plucked from university at 18 thanks to her language skills, Kim spent one year training in intelligence in a secret camp deep in the mountains. She was taught martial arts, shooting, radio communication and how to survive in the wild.

She learned Japanese from Yaeko Taguchi, a Japanese woman she says was abducted by North Korea and with whom she lived with for two years. (Kim has since met with the kidnapped woman's brother and son.) She was then sent to the Chinese city of Guangzhou to perfect her grasp of Mandarin.

Former North Korean spy Kim Hyon Hui arrives for a press conference with Shigeo Iizuka and Koichiro Iizuka, family members of Yaeko Taguchi, on March 11, 2009.

In November 1987, she was suddenly called back to Pyongyang. North Korea's spy agency decided Kim was ready for her deadly mission -- an assignment she received in the dead of night from the agency's highest ranking officer.

Kim and a male accomplice, Kim Seung Il, went to the Austrian capital Vienna disguised as a Japanese couple. It was there they were given the bomb.

"The bomb was a small Panasonic radio, behind that there were ... batteries. North Korea built it so half of it acted as an explosive with chemicals in, the other half could be used as a regular radio," says Kim.

Bomb in radio

They took the bomb to Baghdad. As they boarded the Korean Air Lines Flight 858, destined for Seoul, officials confiscated the batteries in the radio -- without which the bomb was useless.

"I was very nervous at that time," Kim says. "I picked up the batteries, put them back in the radio and complained to the officials. When I turned on the radio, sound came out so I told them they were making too much of a fuss." Officials then allowed Kim to pass through security and board with the radio intact.

"For a moment, the thought of 'these people will die' crossed my mind, I was surprised when I thought that, I felt I was being weak, I was doing this for unification."

Kim put the bomb in an overhead locker and took some pills to relax. She and her accomplice then got off the plane at a layover in Abu Dhabi. The plane carrying 115 people and a North Korean bomb departed for Seoul but never made it.

Wreckage found in territorial waters of Burma, now known as Myanmar, on December 16, 1988

How she was caught

Plans to escape via Rome and Vienna did not pan out as the two agents were detained in Bahrain. They had a plan B -- cyanide pills hidden in cigarette filters.

"We were taught that if an agent fails on a mission, he or she needs to commit suicide. We need to swallow the pill to protect the secret ... we know very well that our families in the North would be harmed, so naturally we decided to swallow the pills. At the time I thought my 25-year-old life ends like this."

Biting into the cyanide pill, Kim lost consciousness but survived. Her male comrade died.

Extradited to Seoul for interrogation, Kim says she denied everything for eight days for fear of retribution against her family, but she couldn't keep it up.

She was put on trial and sentenced to death, but Kim was later pardoned by then-President Roh Tae-woo, despite criticism from the main opposition party at the time.

Roh believed she was as much of a victim of North Korea's brutal regime as the passengers killed on board the doomed Flight 858.

"When I heard I was pardoned, rather than feeling joy of regaining life, I thought of my mother back in the North. How happy she must be if a daughter who almost dies then lives, but I was a big sinner. I should have died," she says.

Agents escort Kim Hyon Hui, with her mouth taped shut, as she arrives in Seoul, South Korea, Dec. 15, 1987, from Bahrain.

After being pardoned, she worked for South Korea's National Intelligence Service before marrying one of her bodyguards.

A mother of two, she has written memoirs about her experiences, donating some of the proceeds to the victims' families.

But some families criticize the South Korean investigation at the time, even questioning whether Kim was the person responsible for the deaths of their loved ones.

It's clear that reliving that time 30 years ago takes a toll on Kim. She fights back tears a number of times but insists she has survived to remind people of what North Korea is capable of -- something she says is particularly important as the Winter Olympics appears to be bringing the two sides together.

"As a living witness to North Korea's terror, I tell the truth and I am on the front line to prevent this kind of attack. Korea is still at war when it comes to ideology and thoughts."