Thinking about it, if the pilot and WSO were both still in their seats when found, whatever overtook them must have been rapid and devastating - an IR seeking shoulder launched jobby doesn't usually pack much of a punch and they usually just shave off a chunk of the jetpipe plus some splinter damage - enough to mission kill the aircraft and perhaps bring it down but they'd have had time to work the problem and probably one or both would have had time to eject.The route published by Turkey, with times, altitudes, & commentary, shows the RF-4 heading NE at low altitude & veering into Syrian airspace for a few minutes. During that time it was warned by Turkish ground control that it was breaching Syrian airspace. It went very close to the Syrian coast, close enough to have been engaged by AA guns, but safely entered Turkish airspace, before turning round & heading SW into international airspace. The pilot informed ground control that he intended to repeat his SW to NE run, but on the correct route avoiding Syrian airspace, & requested ground control assistance to ensure it.
The Turkish account has it hit by something (presumed to be a missile) while on that SW leg, 13 nautical miles from the Syrian coast. It was out of range of any shoulder-launched missile or AA gun, & several minutes & many miles after leaving Syrian airspace, having made a nearly 180 degree change of direction.
I agree that it's possible that optically guided AA engaged it when it was within range but missed, & that's being claimed by the Syrians as the cause of the crash despite the discrepancies in timing & crash location. I presume that if they fired a missile which could have brought down the RF-4 outside territorial waters, they'd rather not admit it.
I'm suspecting more and more we're talking about something with a substantial warhead.
Found this blog which looked pretty interesting that talks about Syrian SAM deployment in 2010.
IMINT & Analysis: Syrian Strategic SAM Deployment