He wrote two beginners’ books, Mitchell’s Guide to the Game of Chess and another book titled simply Chess. Mitchell’s Guide to the Game of Chess contained what may be some of the worst advice ever handed down: ‘When in doubt, move the King’. Edward Lasker revised it in 1941.
In January 1926 the Bulletin magazine wrote, "David A. Mitchell, former chess editor of the Philadelphia Ledger, who has been residing in New England for his health, has moved to Bermuda, where, on Harrington Sound, he finds the climate very mild and expects to spend the winter there."
Not long after that newspapers reported Mitchell had mysteriously disappeared. Mitchell had returned home from Bermuda in March and on the night of his disappearance on a Sunday he gave his neighbor a check for $25, saying it was all he had and he would not need any more. The Philadelphia] Ledger reported, “Northport, Me., June 2 –David A. Mitchell, formerly of Philadelphia, and author of several books on chess, has been missing from his summer home on Temple Heights here since Sunday night. A searching party was organized by Sheriff Frank D. Littlefield today after a note was found at the house.”
In the June 3, 1926 edition The Philadelphia Inquirer carried the following article: "BELFAST, Me., June 2 – Sheriff Frank A. Littlefield and a posse searched the woods on Mount Percival, Northport, Maine, for David A. Mitchell, a Philadelphia newspaper man, who has for the past few years occupied a home near the mountain. Mitchell was last seen Sunday night when he told callers at his home it was the last time they would ever see him and that he was suffering mentally. He had talked of hearing beautiful but mysterious music, and on a card found on his desk was written, 'If he don’t stop that machine I’ll go insane.' Mitchell spent the past winter in Bermuda, returning in March to Northport, and is said to be despondent over the death of his mother a few weeks ago. He has one brother, William L. Mitchell, of Philadelphia. While his house was in perfect order, he took none of his belongings and it is feared he may have drowned himself in Penobscot Bay."
And that's all that is known about what happened to him. I was unable to locate any of his games, but did find this problem:
1.Rxe5 Nxe5 2.Qd4 e6 3.Qh4#
1.Qc8 Qb8 2.Qxb8 Nxe3 3.Qh8#
1.Bc8 e6 2.Rexe5 Ke7 3.Qc7+ Ke8 4.Qd7+ Kf8 5.Qd8#
1.Bg6 e6 2.Rexe5 Nxe5 3.Qc7 Nxg6 4.Qd8+ Ne7 5.Qh8#
1.Bxg4 e6 2.Rhxe5 Ke7 3.Qc8 f5 4.Rxe6+ Kf7 5.Qe8#
1.Bc2 e6 2.Rexe5 Ne3 3.Ra5+ Ke7 4.Qc7+ Kf8 5.Qd8#
1.Bd3 e6 2.Rexe5 Ne3 3.Ra5+ Ke7 4.Qc7+ Ke8 5.Ra8#
1.Bb1 e6 2.Rexe5 Ke7 3.Qc7+ Ke8 4.Rxe6+ fxe6 5.Bg6+ Kf8 6.Qc5#
1.Rh6+ Kg5 2.Rxe5 Nf6+ 3.Kh8 Nh5 4.Qe3+ Nf4 5.Kg7 e6 6.Qg3#
1.Bd7 e6 2.Rhxe5 Nxe5 3.Rxe5 Ke7 4.Qc7 f5 5.Ba4+ Kf8 6.Qg7#