Answer: be irrelevant to the justice or injustice of capital punishment.
Step-by-step explanation:
From the information given, Banks was charged with murder but his lawyer failed to vigorously cross-examine an informant testifying against Banks or to investigate the case.
Based on the above, since Banks may not have received a fair trial because of poor representation, then a retentionist would argue that the injustice in the conduct of the trial would be irrelevant to the justice or injustice of capital punishment.