File photo of Egyptians being deported following the beheading of a group of Coptic Christians by militants after they were abducted from Sirte.

:: Libyan authorities have arrested a suspected ISIS militant they believe was involved in the beheading of 21 Egyptian Coptic Christians in Libya in 2015.

Chief Prosecutor Al-Sadiq al-Sour told reporters on Thursday that the beheadings took place behind a seaside hotel in the coastal city of Sirte. He says authorities have also identified the site where the bodies were buried.

The killings, documented in a grisly video released online by the extremists, shocked Egypt and led it to launch punitive airstrikes.

Al-Sour said ISIS militants have been using Sudan, the country’s southern neighbor, to get into Libya.

Hundreds of ISIS militants are believed to have fled Sirte into the Libyan interior after their defeat last year by militias loyal to a UN-backed government in Tripoli, the capital.