December 10, 2018 10:21 AM EST

Fifteen people who chained themselves to a plane at an airport outside London to prevent the deportation of 60 undocumented immigrants were found guilty of terrorism-related charges in a British court on Monday.

The activists, who are members of campaign group End Deportations, used pipes and chains to fix themselves to the nose of a charter plane at London Stansted Airport in March 2017, forcing the airport to temporarily shut down. The plane had been due to take migrants to Nigeria, Ghana and Sierra Leone, The Guardian reports.

The group, known in British media as the Stansted 15, were convicted of the “intentional disruption of services at an aerodrome” — a crime that carries a maximum sentence of life in prison. They will be sentenced in February.

During the nine-week trial at Chelmsford Crown Court in southern England, the defendants pled not guilty, arguing that the fact that authorities have since allowed some of the would-be deportees to stay in the U.K. showed that their actions were justified.

But prosecutors said that “regardless of their motivation,” the activists had “placed themselves, the flight crew, airport personnel and police at serious risk of injury or even death due to their actions on the airfield.”

The group released a statement shortly after the verdict was announced. “We are guilty of nothing more than intervening to prevent harm,” they said. “The real crime is the government’s cowardly, inhumane and barely legal deportation flights and the unprecedented use of terror law to crack down on peaceful protest.”

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