Amjad bin Sasi was a cocky 23-year-old who didn’t mind his tongue, even after the Islamic State militant group (ISIS) took over his home city of Sirte on Libya’s coast. Last December, ISIS executed bin Sasi for swearing.

His horror story was one of dozens I heard on a recent trip to Libya to speak with people fleeing Sirte, where for the past year ISIS has extended its grip.

Bin Sasi’s capital offense was naming God in a curse while brawling with a neighbor. Relatives told me they suspect that one of ISIS’s omnipresent informants overheard his expletive. That night, they said, ISIS gunmen burst into bin Sasi’s home and hauled him to prison. It didn’t help that when bin Sasi was ordered to repent, he spat at the ISIS judge. Three days after his arrest, an ISIS executioner shot him dead at Sirte’s Martyrs’ Square.

An ISIS official makes an announcement ahead of the execution of two men for “sorcery” in Sirte, Libya. Image from a 2015 Islamic State (ISIS) video. The online clearinghouse Jihadology.net posted the video on its website.

While world attention has focused on ISIS atrocities in Iraq and Syria, the group has made Sirte its third stronghold. It has amassed as many as 1,800 fighters there—most of them foreign—and taken over government buildings and coffers, the military base, radio station, and power plant. ISIS now controls every detail of Sirte residents’ lives, from the length of men’s trousers to the style of women’s underwear. It flogs men for smoking or listening to music, or for failing to pray at the mosque five times a day. It ensures food and medicine for its fighters, but not for residents, even those who abide by its draconian rules.

And then there are the executions, based on largely secret proceedings that negate the most basic fair-trial standards. Two men were decapitated for “sorcery.” Others were shot in the head because they were Coptic Christians or because ISIS decided they were spies. ISIS hung some of the corpses from scaffolding for three days, their orange jumpsuits a grim allusion to Guantanamo.  I tallied 49 unlawful executions  since ISIS began capturing Sirte in February 2015. I am confident there were many more.

“Life in Sirte is unbearable. Everyone is living in fear,” said “Ahlam,” who like most residents I interviewed was scared to let me use her real name. Ahlam spoke with me in the Libyan city of Misrata, where she had come for medical care. She cried as she said she would have to return to Sirte. With no shelters in Libya for people fleeing ISIS, and no savings, her family had nowhere else to go.

What’s shocking is not only what ISIS does in Sirte, but that it took the city with seeming ease. Internal chaos enabled this move. Libya now has three rival governments—two backed by warring militias with documented records of human rights abuses and a third, United Nations-backed body that is strugglingto gain authority. But international neglect helped as well. A NATO intervention in 2011 ostensibly aimed to protect civilians from the brutality of Libya’s then-leader, Muammar Qaddafi, but failed to help the country emerge from four decades of erratic, authoritarian rule. US President Barack Obama in April called inattention to Libya after 2011 the “worst mistake” of his presidency.

The United Nations Security Council also has failed Libya by not acting on repeated promises to identify and impose sanctions on the country’s many perpetrators of war crimes and other serious abuses. Member nations of the International Criminal Court, which has jurisdiction over war crimes and crimes against humanity committed in Libya since 2011, also have taken a pass, failing to provide the court with sufficient resources to investigate grave crimes there.

The international community should get serious, now, about ending impunity in Libya. Armed groups there commit murder and other atrocities with abandon because they know they can get away with it.  Now world powers including the United States, Italy, the United Kingdom and France are seeking to arm the UN-backed government to oust ISIS. Any actions they take need to also foster respect for human rights and the rule of law. Otherwise odds are that the Libyan people’s suffering will just assume a new form under a new set of abusive rulers.

While the international community ponders next steps, bin Sasi’s family still awaits his body. “ISIS said, ‘He is kafir [a non-Muslim], so you cannot bury him in a Muslim cemetery,’” said one relative, “Ibrahim.” Asked what his message was to the rest of the world, Ibrahim replied, “We want to get rid of ISIS.” Then he added, “And we want justice.”