The bottom line is that we still don’t quite know what happened. Did some Muslim Brotherhood members try to storm the Republican Guards HQ after dawn … or did the military open fire on praying protestors? A helpful summary from the Guardian:

The Egyptian military says gunmen from an “armed terrorist group” and linked to the Muslim Brotherhood – the Islamist organisation with which Morsi is affiliated – tried to storm the building shortly after dawn, firing live ammunition and throwing firebombs, killing one police officer. But the Muslim Brotherhood said troops opened fire at protesters, including women and children, none of whom had attacked the troops. The Guardian’s Patrick Kingsley spoke to a number of witnesses who gave differing accounts of what happened. Accounts from five of the wounded backed the Brotherhood’s version of events.

The NYT has this detail:

Bullet holes in cars, lampposts and corrugated metal barriers indicated that gunfire was coming from the top of a nearby building where the sandbag barriers around makeshift gun emplacements were visible. Bullet casings on the ground and collected by Islamist demonstrators bore the stamp of the Egyptian Army. But Egyptian state television showed film of a pro-Morsi protester firing what appeared to be a homemade handgun at advancing soldiers from behind a corner about 250 yards away. The footage was in daylight, hours after the initial attack began. A witness who lived nearby said he saw two men with similar weapons among the protesters.

The protesters, witnesses and video footage all appeared to portray the pro-Morsi demonstrators as attempting to fight back against the soldiers by throwing rocks.

It seems insane to me that, holding power and needing some Islamist support, the military would then engage in an unprovoked slaughter of protesting Morsi supporters at prayer. And yet the slaughter seems beyond anything we have yet seen since the start of this turbulence. I tend to agree with Juan Cole, until we get further evidence:

Both narratives are problematic. The army’s description of a “terrorist attack” sounds propagandistic. The Brotherhood account doesn’t indicate a motive for the army abruptly to launch an attack on peaceful demonstrators.

But this does, from the army spokesman:

The scene spiralled out of peacefulness at about 4am, he says. An armed group attacked the perimeters around the Republican Guard HQ, and the personnel responsible for securing the premises – from the army and police – were attacked by live ammunition, Ali says.

At the same time other groups started to climb up the buildings nearby and throw stones, molotov cocktails, bombs and heavy objects, Ali says, resulting in the death of one army officer and the injury of 42. Many of them are in a very critical condition, he says.

Stay tuned.

(Photo: The bodies of men lie on the floor of a morgue at the Liltaqmeen al-Sahy Hospital in Cairo’s Nasr City district, after allegedly being killed during a shooting at the site of a pro-Morsi sit-in in front of the headquarters of the Egyptian Republican Guard on July 8, 2013 in Cairo, Egypt. By Ed Giles/Getty.)