McCarthy was found guilty of killing her neighbor after saying that she was coming over to borrow some sugar. Police found McCarthy's DNA on a butcher knife left at the crime scene, which she apparently used to stab and cut off her neighbor's wedding-ring finger. Police then found McCarthy's name on a pawn-shop receipt where the ring had been sold.
The impartial-jury rights guaranteed by the sixth amendment come under review in cases like this often — and serve as a judicial lightning rod each time they do. According to a recent study by professors at Carnegie Mellon, Duke, and Queen Mary at the University of London, the difference between one, two, and three black jurors can make a huge difference:
In cases with no blacks in the jury pool, black defendants were convicted at an 81% rate and white defendants at a 66% rate. When the jury pool included at least one black member, conviction rates were almost identical: 71% for black defendants and 73% for whites. The impact of the inclusion of even a small number of blacks in the jury pool is especially remarkable given that this did not, of course, guarantee black representation on the seated jury.
In the Texas country where McCarthy's crime was prosecuted, however, the representation argument doesn't hold up as well. According to a letter her attorneys sent to Governor Rick Perry requesting a reprieve of the death penalty, the racial make-up of the region appears more stark than the national averages cited in the study. Per The Guardian:
The lawyers argue that such a striking imbalance was wholly consistent with a systemic discrimination in Texas, and in Dallas County in particular, towards white juries in capital cases. The county is 23% black and 69% white, yet of the 81 people from the area who are on death row or who have already been executed, 42% are black, 21% are Latino and 49% are white.