Yale Law Journal
Legal rules severely restrict payments to fact witnesses, though the government can often offer plea bargains or other nonmonetary inducements to encourage testimony. This asymmetry is something of a puzzle, for most asymmetries in criminal law favor the defendant. The asymmetry seems to disappear when physical evidence is at issue. One goal of this Essay is to understand the distinctions, or asymmetries, between monetary and nonmonetary payments, testimonial and physical evidence, and payments by the prosecution and defense. Another is to suggest ways in which law could better encourage the production of evidence, and thus the efficient reduction of crime, with a relaxation of the rule barring payment.
Saul Levmore & Ariel Porat, "Asymmetries and Incentives in Plea Bargaining and Evidence Production," 122 Yale Law Journal 690 (2012).