The Horrifying True Story Behind Netflix's '22 July' : How a Rogue Terrorist Massacred 77 People

For the 600 Norwegian youths gathered on Utoya island for five days of fun, sun and lively political debate, the first shock on July 22, 2011 came when they were told a bomb had just exploded in Oslo outside the building that houses the prime minister’s office.

“We thought Utoya was the safest place to be,” Ingvild Stensrud, 16, would later recall to PEOPLE.

As the campers, mostly teens affiliated with the Labor Party, digested the distressing news, a 6-ft.-tall blond man clad in a police uniform arrived 90 minutes later on the island by boat, raised an assault rifle and opened fire.

For more than an hour, then 32-year-old Anders Behring Breivik, a rabidly conservative, anti-immigrant fanatic, plucked off the youths as nonchalantly as if they were apples from a tree. By the time a SWAT team arrested Breivik — who later confessed — Norway had endured its worst day of violence since World War II: 69 died at camp, 8 in the bombing.

The horrifying attack is at the center of new Netflix movie 22 July — a dramatic retelling of the traumatic events that changed Norway forever. The movie is directed by Paul Greengrass, who is also behind United 93, Captain Phillips and the Bourne franchise.

WATCH: 22 July Official Trailer

The attack started with a car bomb outside Prime Minister Jens Stoltenberg, which killed 8 people and injured at least 209. Two hours later, Breivik took a ferry to the island dressed in a homemade police uniform. Greengrass explores how the gunman methodically fired on the campers for almost two hours, taking plenty of time to reload weapons and go tent by tent while finding his victims.

“I watched as he slowly lifted up tent flaps and shot the people inside,” then 21-year-old Adrian Pracon, a worker on the island, told PEOPLE at the time. “At one point four people approached him, thinking he was a real policeman. I saw one of them say, ‘Thank you, you’ve come to help us.’ He shot all four of them.”

WATCH: Norway Is the Happiest Country in the World

In the end, Breivik was swarmed by S.W.A.T. police and forced to surrender after killing 69 people and injuring 110. He was later tried in a trial that captivated the country as the right-winger reportedly claimed he wanted to eliminate the next generation of the democratic party. Breivik also spouted anti-Islamic beliefs and claimed being a hero for trying to stop them.

Breivik was sentenced to 21 years of containment, a type of imprisonment that can be extended indefinitely.

22 July is streaming on Netflix now.