What may be a martyr to some is just a dead, gone and soon forgotten person to others. Besides the proceedings have to be reviewed by an Army general and he/she will make the "binding decision" on whether to accept the verdict and sentence, that may take a few months, then Nidal can appeal (even if Nidal doesn't want any appeals, some are a matter of procedure) and that can take years. It has been more than 50 years since the military has executed one of their own.
Also the Afghan incident involving Army Staff Sgt. Robert Bales and the murder of the 16 Afghan civilians, he received life because he pleaded guilty and avoided the death penalty.