There was actually nothing other than popular media reports and Malaysian propaganda to suggest that the captain crashed the airplane. Most of what was given was speculation, and fairly wild stuff at that.
Oceans are very big places with no radar coverage and spotty communication. Lots of places to disappear.
On Lithium batteries; I got onboard for a trip to Afghanistan some years ago, and saw pallets stacked inside containers from one end of the main deck to the other. I walked the cargo and noted big stickers on the pallets, which were stacked two high, saying "DO NOT STACK." Upon closer inspection, I found that the entire load was lithium batteries.
I called home plate and was told "it's just a three hour flight, and they really need the batteries." I refused the flight, made them offload everything and remove half the pallets. I was told that if it would make me feel better, they could just remove the stickers, and that future flights would simply have the stickers removed. Not on my flights.
On another trip, originating in Amsterdam (for me) headed westbound, I found the hazmat buried halfway down the main deck on the far side of the airplane, instead of up front. It included half a pallet of lithium batteries, with a 30 gallon drum of an accelerant on top, on it's side on a 45 degree angle, so all the pressure of the weighted edge bore directly on the batteries. It was surrounded by packed-in accelerants of various types, all mixed on one pallet. I refused the flight; pull it off, correct it, and put it up front where we have access. They did, unhappily.
I was born yesterday, but it was pretty early in the day.