You can tell by the high-quality video it was done by the Islamic State’s propaganda arm, which is run by an ISIS operative from my state, Massachusetts.

Via ABC News:

Recent moves by the Islamic State of Iraq and Syria [ISIS] to assert itself in Libya have led to clashes with al Qaeda-affiliated jihadis there, experts say, and Egypt stepped into the fray Monday by launching new airstrikes against ISIS targets in Libya.

On Sunday, core-ISIS officially anointed its Libyan affiliate by releasing a savage new video of camouflage-clad jihadis dramatically slicing the necks of 21 Coptic Christians from Egypt who were abducted in Libya.

The video had similar graphics and cinematic flourishes to ISIS’ other major pieces of propaganda from Syria and Iraq, including track and crane camera moves as the victims in orange jumpsuits compliantly knelt in the wet sand of a Mediterranean beach for their final living moments as stars of the Libyan ISIS affiliate’s debut.

While ISIS has increasingly been publicizing its presence in Libya — and worrying many U.S. counter-terrorism officials, who say Western leaders have been too distracted by such hostage execution videos themselves — the group’s expansion is meeting resistance from the clearly dominant jihadi groups there with ties to core-al Qaeda, experts say.

“Because ISIS is so brazen in what they do and their propaganda machine is so prolific with videos like this, it’s easy to see where their fighters are and what they’re doing,” Thomas Joscelyn, an ISIS expert and senior fellow at the Foundation for the Defense of Democracies, told ABC News. “Al Qaeda and their allies try to hide what they’re up to. They don’t advertise it with videos.”