I fail to see any correlation, whatsoever, between MLM and this captain: one has absolutely nothing whatsoever to do with his actions.
Also, to state that one cannot be "normal" one day and then go off the deep end the next, is faulty thinking. It happens. And it happens on a daily basis to people who appear "normal" beforehand. Believe me, I know.
The warning signs were probably there all along. Either they were ignored or swept under the proverbial rug. But the day of reckoning was coming on like a homeward bound freight train. Most unfortunately, this freight train wrecked.
I do, however, see a correlation between this airline captain and his observed behavior and U.S. Army SSgt. Robert Bales. Both suffer from extreme forms of mental illness. And in the case of the airline captain, the outcome could have been a lot more extreme than the disaster created by SSgt. Bales.