Some developments from yesterday: The Russian airline operating the Airbus A321 is Kogalymavia. Police have already begun searching their offices in Moscow, seizing computers and documents.

Both black boxes have been recovered. (one is for cockpit voice recordings and one records flight data.)

There's no indication of technical failure from the tracking of the plane.

Minister Hossam Kamal said there had been no sign of any problems on board the flight...."Up until the crash happened, we were never informed of any faults in the plane, nor did we receive any SOS calls," he said. All contact with air traffic control had been normal, and pre-flight checks showed no problems, he added.

The plane went off radar about 23 minutes after takeoff, and fell near Hasana, Egypt.

At 4:12 GMT it was at an altitude of 33,500 feet and and had a speed of 404 knots. At 4:13, when it went off radar, it had dropped 6 thousand feet and the speed decreased to 93 knots. You can watch the replay here. More here.

There were "very big changes" in vertical speed the last 20 seconds. The plane was set to autocruise at 32,000 feet.

The plane crashed at 4:17 GMT according to Airbus's official statement. While it could be a stall, which calls for the pilot to drop the nose to reclaim speed, that's by no means a given.

Ansar Beit al-Maqdis was Egypt's most violent militant group. It swore allegiance to al Baghdadi in November, 2014. Since then, Wilayat Sinai has claimed credit for firing rockets into Israel in July, and killing 64 Eqyptian soldiers in a massive attack. In addition to manpads, ISIS has gotten hold of the more powerful Russian-made Kornet anti-tank missiles which Russia sold to Syria and Iraq.

Israel just began using a anti-missile defense system in its airlines to protect against attacks by manpads.

Why did the plane crash? The answer for now, is no one knows.

It could be as simple as the plane stalling after it reached cruising altitude and the pilot started corrective action but was unsuccessful. That happened to this Air Asia flight in January. It was an Airbus 320 from the same family of Airbuses as the Russia plane.

Or, it could have been on-board sabotage by either the pilot or copilot. Maybe one had recently become enamored of ISIS, decided to turn the flight into a murder-suicide mission and disabled the other. Maybe one or two passengers disabled both of them and took the controls.

The absence of a missile attack on the plane or an on-board bomb doesn't rule out ISIS' passive or active participation -- nor does it confirm pilot error or a technical glitch (although inadequate pilot training has been a focus of late.) I'd start with the premise that it's very rare for planes to simply fall out of the sky by themselves, look at other cases where it's happened and wait for information from the black boxes. I'm not sure who's lowest on the credibility scale: ISIS or the Governments of Egypt and Russia.