That's why this case is interesting from a legal perspective. The case would not have gone to the grand jury if there was any shred of Texas law for which the DA could get cover for ignoring it. Since he didn't have the law, he had to convene the grand jury, despite his misgivings about it.

Since your quote is very true, the fact that he failed to get an indictment tells me that he convened the grand jury just for show and never made a serious case for the indictment.

Personally, I would think that any DA worth his stones could get an indictment in this case, since I doubt Texas law allows any citizen to leave his abode and seek out a DB with a gun and then take him out, notwithstanding the fact that the DB is firing on a police officer.