As I am in the process of re-reading Harper Lee's To Kill a Mocking Bird, I did a bit of elementary research on the subject of jury selection in Alabama. I discovered that in the Scottsboro boys case (1932 to 1936) the Supreme Court eventually ruled that the absence of African Americans from the jury pool denied the defendants due process. What interests me is in what techniques were employed to exclude people of African descent.
Traditionally most municipalities in the USA select their jury pool based on their state's voter rolls. That is in fact how Alabama does it today.
This is probably chiefly for convenience sake. A state's voter registrations is about the only convenient database of "of age" residents and where they live that the state (and everyone in it) has access to. Particularly back before the computer age. However, it does have the side effect that if your voter rolls are skewed, your jury pools will be as well.
Alabama of course had very skewed voter rolls in the early 20th Century. From about 1890 to 1965, Jim Crow was the rule in the South, including Alabama. Almost no black Americans could vote.
Those who could not vote were not eligible to serve on juries and could not run for local offices. They effectively disappeared from political life, as they could not influence the state legislatures, and their interests were overlooked.
The typical methods used were poll taxes and literacy tests. Both tended to include grandfather clauses that gave a free pass if you were related to someone eligible to vote the year before slavery was abolished (a clever, if transparent, bit of legal trickery). In practice, both tended to be selectively applied to only black applicants. It didn't stop there though, in addition to numerous other onerous requirements, in Alabama you got "doxed" as well:
Your name was published in the local newspaper listing of those who had applied to register. That was to make sure that all of your employers, landlords, mortgage-holders, bank loan officers, business-suppliers, and so on, were kept informed of this important event. And, of course, all of the information on your application was quietly passed under the table to the White Citizens Council and KKK for appropriate action. Their job was to encourage you to withdraw your application — or withdraw yourself out of the county — by whatever means they deemed necessary.
So southern blacks were effectively living in a terrorist state.
This is of course the essential backdrop to Harper Lee's To Kill a Mockingbird.
Your statement is incorrect on two counts. First of all, it is not true that the "absence" from the pool denies due process. Secondly, the violation is not of the Due Process clause of the Constitution, it was held to be a violation of the 14th Ammendment. The violation itself occurs when potential jurors are deliberately excluded from the pool. If by chance they are not present, it is not a violation. This is what it says in a contemporary legal handbook:
While a negro charged with crime is not entitled to a negro jury or to a mixed jury, the federal Constitution guarantees him against any discrimination against the negro race in the selection of a jury by whom he is to be tried.
The problem was that it was a common practice in some places for jury commissioners to exclude so-called "negroes" from jury pools on the grounds that they were unfit to serve as jurors. In places where this was occurring, courts routinely overturned verdicts as violations of the 14th Ammendment.
The mechanism of this exclusion is that the jury commissioner would send summonses only to citizens in well off neighborhoods and if a black showed up accidentally the commissioner would just excuse them immediately.