When the bodies of 24-year-old Louisa Vesterager Jespersen of Denmark and 28-year-old Maren Ueland from Norway were found at a camping area in the Atlas Mountains in Morocco on Monday, authorities first considered it a random act of sick violence that was likely sexually motivated. One of the women was found inside the pair’s brightly colored tent. The other, who had been beheaded, was found a short distance away. Both had been mutilated. Investigators say they were both sexually assaulted.

Now authorities say the macabre murders were linked to Islamic extremist inspired terror after a suspect arrested in connection with their deaths was found to have ties to ISIS, according to a statement released by the Rabat public prosecutor’s office. One of the men reportedly dropped his ID when he fled the area, which led to his arrest.

On Thursday, the Danish intelligence agency authenticated a video that has been circulating online showing the actual murder of one of the women while the other let out a blood-curdling scream.

Local television station 2M reported that a group of four men were caught on surveillance tape pitching a tent near where the women had camped out during a trekking adventure about six miles from the hilltop village of Imlil. The men left the area after just one night.

The women were earning degrees in “outdoor life, culture, and eco philosophy” from the University of Southeastern Norway, west of Oslo. The trekking adventure was apparently not part of their studies. “What we know is that they were on a month-long, private holiday in Morocco,” the university said in a statement. “Our thoughts go to the families.”

Jespersen had posted a message on her Facebook page before the fateful journey asking for advice before she and Ueland departed, according to local media reports. “Any of you guys whos around by then or any mountain friends who knows something about Mount Toubkal?” Her Facebook page has since been taken down.

Investigators from Denmark are traveling to Morocco to assist in the investigation.

Four suspects have been named by Moroccan authorities, but only one has been arrested so far. He was picked up in a busy tourist neighborhood in Marrakech earlier this week. “We are working to bring before justice three other suspects on the run,” according to a statement from Boubker Sabin, a spokesperson for the Marrakech police.

Ueland’s mother told Norwegian television station NRK that she had warned her daughter to be safe traveling in Morocco. Jespersen’s mother told a local media outlet that she had warned her daughter not to go on the trekking adventure.