I'm relatively sure at the plane did crash because of mechanical failure because:
1)the plane crashed in an empty field meaning it was the brave actions of the pilots crashing it into a clear field, if it had been shot down they would have not been able to do this.
2) Look at the pictures the fuselage is pretty much intact concurrent with a crash if it had been hit by a missile their would be debris spread over miles and it would be severely damaged and broken up, anyone who has ever seen a missile target on a fighter will see the devastating effects.
3)BOTH pilots survived, again if it had been a missile strike you would expect them not to.
4) The F-15E Strike Eagle is an EXCEPTIONALLY good strike/superiority fighter, one of the best in the world, and has an extremely impressive kill ratio which I believe is 0-200+ enemy fighters. Meaning in it 20+ hrs in service it has NEVER been shot down and it has gone against more capable systems than the lianas have. The Iraqi ADS was far more deadly than the Libyans and the Bosnian ADS was inventive enough to shot down a F-117 (although no one knows how) but NO F-15' and since then the F-15s have undergone extensive upgrades.
it is for these reasons (^^) that many in the pilot community do believe it crashed due to mechanical failure. (independent sources)
Any fighter no matter how advanced can crash just look at the Su-30MKIs, F-18/F,B-2 Stealth Bomber ($2.2 BN) there could be any number of reasons these planes are made up of tens of MILLIONS of parts and only a few need to fail to lead to a catastrophic accident. Although the F-15s have a remarkable safety record with extensive redundancy systems it is not infallible.
+ can anyone give any information on the rescue of the 2 pilots, was it conducted by USAF CSAR (Pararesceumen, PJs) I mean that is their primary job and they are VERY good at what they do but were they deployed in the area? Or was it USMC/USN SAR who have assists in the area operating of LHDs/LPDs/ACCs? The fact that both pilots were rescued so fast is very impressive and unique to the US, no other country has such reach.
P.S if you actually watched the news you'd see it was Britain and France that pushed the UN for a no-fly zone whilst the US took a removed position until the UN resolution was passed then took the lead because it offers unique assets and reach that no other country on earth can provide. This is why they now that they have taken out the ADS they want to hand power over to someone else. Public opinion in the US is not too strong for this interdiction and the painful shadow of Iraq still hangs over many Americans.