Re-posted here May 11
minor edits Jan. 1 2012.
Resolved to Protect Benghazi
Talk of seizing the Libyan skies started early in the civil war, fed in large part by the impression that Gaddafi's insane forces were bombing peaceful protesters from the air (still no evidence). Considering real atrocities, like the 130 government soldiers executed around al-Baida for refusing to shoot protesters (we heard), bloodbath and madness loomed. The world had to act, it gradually became clear, as they had in Yugoslavia, Iraq, and elsehwere, by seizing the skies away from the repressive government and using this high ground themselves for "policing" powers. Responsibility to Protect, P2P, it's called. Respond to Panic is more accurate.
Three weeks into the insurrection, it was getting desperate for the rebels. They had pushed too far and been left too long as the regime pushed back. One-by-one, cities west and then east fell back to government hands, and by March 17 loyal forces were moving in on Benghazi itself. Gaddafi had promised to go to Libya's second largest city and the de-facto rebel capitol, and crush those who refused to surrender. That coming to fruition would destroy any reasonable hope of finally toppling the colonel with this insurrection.
United Nations security council resolution 1973 was voted in 10-0 at the end of a late-night session on the 17th. It called for a "cease-fire," with special emphasis on government actions. But it was never in fact to be applied to the rebels, and became a one-sided cease fire demand. The resolution also tightened sanctions, froze assets, and imposed a "no-fly zone" for government aircraft, over the whole nation.
The skies were authorized to be seized as of morning light on the 18th. As the west prepared to attack and scheduled a special meeting in Paris, Libya announced a cease-fire in the evening. The world scoffed, and noted that government forces were still rushing towards Benghazi. No one bothered waiting for the rebels to agree to stop shooting, and they never did. They couldn't topple anything without firing a whole lot more.
There is some confusion, but not as much as there should be, about the supposed siege of the city starting on the morning of the 19th. The new Wikipedia page for "the second battle of Benghazi" has the first shots fired, by Gaddafi's forces near the city, at about 7:45 am.  The government denied any attack on Benghazi, that hey held their positions miles away. But shelling of the city's southern areas occurred, and scores were killed and injured, according to hospital staff, Even two air strikes were reported in the early morning hours by one reporter. Gaddafi troops were fought at the gates, said one rebel commander, and government tanks were roaming freely inside the city, according to many reports.
The evidence of heavy weapons usage in the area, including Libyan army tanks seems entirely credible, but there are no photos of these attacking forces to show their context. Considering this abandoned army base on February 24, the rebels had heavy weapons early on and numerous tanks, among other things, after this siege. And the government claimed with a straight face they did none of that, that it was apparently the work of rebels with seized equipment shooting at each other to draw in the West.
Whichever the case, the West was trying its best to be drawn in. Very wealthy leaders of some handful of normal countries (US, UK, France, etc.) talked it over in Paris. By the middle of the day an urgent consensus was reached to save Benghazi by starting to enforce the 36-hour-old resolution 1973. A rather lopsided vote from 9 of the 22 members of the Arab League had already been managed, bolstering the surface-level worldliness of this trojan horse air campaign. Asked if military action would now go ahead, the British Prime Minister David Cameron said:
"Gaddafi has made this happen. He has lied to the international community, he has promised a ceasefire, he has broken that ceasefire, he continues to brutalise his people, and so the time for action has come."Fire in the Sky: A Government Air Attack?
The pilot was seen to eject from the flaming jet with a parachute rather late in the sudden nose-down plunge. On impact with a residential area, a massive, dull orange fireball crusted with black expanded over the sururb and stretched into a tower of black smoke. Citizens of the rebel capitol reportedly cheered and celebrated as the jet crashed. 
The photo was run in huge sizes by countless news outlets that day, visualizing the situation in appropriately stark and dramatic terms. As Sky TV put it, "the aircraft crash in Benghazi appears to be the first solid evidence to contradict Libyan claims of refraining from military action." The solemn decision reached in Paris came "just hours after a Libyan ceasefire was broken" by this crash, reported The Sun. "Gaddafi appeared to openly flaunt the threat of a no-fly zone resolution earlier today as a fighter jet was shot down..." 
The Telegraph's Rob Crilly in Benghazi, was on the roof of a hotel where journalists stay when he saw the fighter. In a blog entry at 9:21, he wrote:
It came in from the sea, somewhere to the north. At first the residents of Benghazi cheered, believing it would herald the start of air strikes against Gaddafi forces still rumbling towards their city. “Is it European,” shouted one. Then it swung back around the city, describing, a high, slow circle even as artillery shells pounded the outskirts of the city. If it was a Mirage then maybe it was one of Gaddafi’s last.It's still speculated that catastrophic engine failure caused this crash, but that's an odd enough coincidence, and enough reports suggest the sound of anti-aircraft fire, that I'm presuming it was torn down with guns on the ground. Again, the government of Libya denied this was their jet on any mission for them, that they didn't intend to flaunt anything at just that moment.  Again, the world didn't believe the civilian-bombing regime.
It’s next run would have been more deadly, as it roared back across the city, this time flying low and straight – the very definition of intent – as anti-aircraft guns roared along its western path. [...] A flash illuminated the jet, somewhere near its tail. The flash grew to a flame as an explosion ripped through the plane, stopping it as if caught by an invisible hand rather than anti-aircraft fire. Slowly the plane sycamoured towards the ground where it exploding in another, bigger fireball. 
Friendly Fire in the Sky? A Rebel Attack?
Just before noon, the Telegraph reported "confirmed reports from Libyan rebel leaders that the jet fighter shot down today over Benghazi was one of theirs, and not a Gaddafi aircraft."  The Guardian's Chris McGreal said as early as 9:45 "Some of the rebels say it’s their plane. It might have been their only plane that was shot down by Gaddafi's forces," adding at 10:19 "the rebels now concede it was their only plane."
The protesters-turned-rebels were swooping over the city "low and straight – the very definition of intent"? And who shot their air force down? Previously it was presumed to be anti-aircraft fire from within the city. I could swear I saw a few whispers that it could have been friendly fire, in trigger happy wild west Benghazi. But I’m having a hard time relocating them now, aside from Rob Crilly, "tweeting" around 11:30 “rebels [are] telling us they think the plane shot down was a rebel plane – fog of war. We only saw one." 
A Government Attack on the Rebel Attack?
Most source leapt straight from rebels killing Gaddafi jet to Gaddafi killing rebel jet, either one meaning Gaddafi, but not the rebels, was in violation of the cease-fire-no-fly/whatever demand. Rick Leventhal told Faux News at mid-day "we don't know" who was flying the jet. If it were Gaddafi's fighter, it'd be in major violation just for flying there. But if it was a rebel jet, it was probably just aiming for the government tanks in the city, which he said "we believe" were targeting the journalists' hotel.  But if it had been a government jet, it may have been aiming itself for the hotel. Maybe the tanks were rebel-held and there to shoot down the plane.
Sky News' Emma Hurd said "suspicions have now been raised that the jet was a rebel-flown, stolen aircraft hit as it sought out Gaddafi's forces on the outskirts of Benghazi. ... There is still some confusion over that but what is clear is that despite claims of a ceasefire there still is fighting and it seems to be led by his [Gaddafi's] forces." 
Considering again the somewhat unclear location of government forces on the 19th, it needs a bit of presumption to take the rebel version that they were at and in the city. But this is all but necessary to accept they were close enough to shoot down the mystery jet. And, of course, that would also put them close enough to be targeted by it. Within just over a day, the no-fly-zone against the government of Libya became, effectively, a no-shooting-at-rebel-air-offensives-zone. That, I believe, is unprecedented.
The Sydney Morning Herald reported a bit later in the day:
However a rebel official reached by telephone acknowledged the plane was one of their Mirage fighter jets and that it had been downed by loyalists. "It was one of the insurgents' planes. It was downed by Kadhafi's forces. From what I hear the pilot is dead but I cannot confirm that," he said. Aircraft Model
The rebels held very few acknowledged aircraft at this time. Most people believed the number was zero, leading to the presumption that it was from the government. As noted above, Chris McGreal passed on rebel reports, multiply confirmed, that this "was their only plane." 
The rebel official had cited it as one of a few, and gave it as a French-built Mirage (unspecified model). The Telegraph however noted this was "contrary to other reports that it was a Mig-27 Flogger-D."  One should hope that a rebel official giving specific information would know the make. David Crilly, citing rebel sources, said "no-one able to ID it. Consensus was that it wasn’t a mig – possibly a mirage." 
Comments at the New Statesman suggest the craft was not a Mirage. Someone there so inclined did suggest the F-1 as compatible, the only specific model I've seen specified.  Other said Mig-29, and "visual identification confirmed: it's MiG 23." Live Leak's report and Wikipedia called it a Mig-23.   This is supported by further sources, but that's perhas not it either.
I decided to overlay the jet photo with schematics of the Mirage F-1, Mig 23, and the Mig-27 Flogger D. I used perspective and skew effects on the photo to make it as "flat" as possible in overall proportions like these overheads (planar surfaces anyway, wings and horizontal stabilizers). Then I matched the body, nose-cone to tail-fin, as close as possible, and found all of them are reasonable fits, but the Mig-27 is the only one that seems perfect (note also the "shoulder spikes." likely off due to rotation). Then I looked at the wings. Both Migs have adjustable ones, but the sweep setting here also mimics the F-1's fixed angle. For size and shape the wings are a best fit best with the Mig-27, and is clearly out for the Mirage. The Telegraph had it.
update April 12: I re-did the graphics. The plane was a bit too wide before. For reference, the original version is here. Also, the rebels were recently caught flying a MIG-23, which NATO escorted back to the ground for violating the no-fly zone. Still no sign of them running any of the model used that morning. [source]
I'll spare myself (for now) the painful research of seeing just what this model means vis-a-vis Gaddafi's air force, rebel-seized Gaddafi jets, and related implications. Others better informed may perhaps have a comment to share on that.
The Wreckage and the Crew
Seen from a distance, the mystery Mig seemed to plow straight down into a residential neighborhood, and engufled it in a massive fireball. A few deaths, many injuries, and much damage should be expected. It took two days for Fox News's correspondent Rick Levental to be shown the wreckage on the afternoon of the 21st. He testified the plane was definitely rebel, painted with the old monarchy flag on its tail-fin. Dull metal sheet and engine debris was strewn around a rather large walled courtyard of an “old adoption home.” 
What if the government forces truly were too remote to have taken that shot? Only the rebels would then have controlled the ground fire in that area, as first noted in the presumption they had shot it down. They controlled the jet itself, as we found out, so absent AA fire from Gaddafi’s side, it was friendly fire, rebel-on-rebel. This seems most likely, in fact, going just by logic. But that contradicts rebel findings. ... Oh well.
But what if this wasn’t accident? All things considered, it probably was, but my over-active imagination has me wondering if it could possibly be a false flag bit of theatrics for the foreign journalists and their cameras. Perhaps it went awry, or was re-written behind the lead actor's back. Maybe the original idea was so strafe or rocket the hotel and massacre journalists, before zipping away from the hapless civilians' defenses. The rebels would clearly not have claimed it in that case. The possibilities are endless when you have a case this full of holes and mystery.
On the Mig/Mirage confusion, I would guess the rebels did in fact hold a very few Mirages, acknowledged, and at least the one Mig-27, unacknowledged as far as I know. If this were the case, we should ask why rebels were flying a model of jet they don't acknowledge having? Considering the first impressions that it was Gaddafi's jet, maybe it was to create that first impression? The painted tail-fin mitigates against this, but for all we know, that was painted on after the fact, to support the story they adopted, for whatever reason, if it differed from the original story, written by whoever ...
The Telegraph's Crilly said he saw the Mig-27 first come in, and the line of travel suggested “it came in from the sea, somewhere to the north.” Western airpower was sitting out there on carriers, ready to launch. It’s odd to suspect Gaddafi’s forces would launch from out on the sea or even swoop out much over it and risk shoot-down. The same might go for a rebel jet on its way to attack Gaddafi’s forces or … whatever it was “intent” on doing. Is it possible a rebel jet - or even a remote-controlled drone - was launched from naval points north? The photos of the pilot ejecting only shows a parachute and a large object from the distance seen. Again, the possibilities are endless...
Whatever was really going on there, this mysterious incident certainly wasn't the cause of the bombing raids and 110 cruise missile strikes that started later that day. It did, however, serve a nice role tipping the scale in the public mind's eye. Gaddafi never stops flaunting, will never stop the killing and the insanity on his own, but now he will go down in flames. It started to really happen with jets that were French Mirages, to much cheering, a bare eight hour later, seeking out Saddam's forces - still stationed miles from the city.
 Second Battle of Benghazi - Wikipedia, the free encyclopedia
 Live Leak March 19
 "PM: The time has come for action" The Sun. March 19. http://www.thesun.co.uk/sol/homepage/news/3478243/Jet-shot-down-over-Libya.html
 Libya as it Happened: March 19. The Telegraph. http://www.telegraph.co.uk/news/worldnews/africaandindianocean/libya/8393509/Libya-as-it-happened-March-19.html
 Libya military action - Saturday 19 March part 1. The Guardian. http://www.guardian.co.uk/world/blog/2011/mar/19/libya-live-blog-ceasefire-nofly
 Libya live blog: latest developments on no-fly zone, ceasefire and ...
 Fox News. Coverage of Libya war, dispatch, Rick Leventhal. March 19. http://video.foxnews.com/v/4595510/rick-leventhal-live-from-libya
 Fox News. Coverage of Libya war, dispatch, Rick Leventhal. March 21. http://www.foxnews.com/world/2011/03/20/significant-success-early-stages-enforcing-sanctioned-fly-zone/