[mig39]

That could explain one accidental shootdown. It cannot conceivably explain three.

[altairprime]

How easy is it in an F-15E to modify a friend to a foe in the targeting systems?

[nradov]

The IFF system will trigger warning symbology on various cockpit displays but it won't prevent the pilot from employing weapons. At this point we don't know for certain whether IFF was enabled and working correctly on any of the aircraft involved.