The Limitations of DNA Evidence in Innocence Cases

Death-sen­tenced pris­on­ers with cred­i­ble evi­dence of inno­cence have gained sig­nif­i­cant atten­tion this month with the exe­cu­tion of Marcellus Williams in Missouri, the near-exe­cu­tion of Robert Roberson in Texas, and the U.S. Supreme Court argu­ments in Glossip v. Oklahoma. There is a com­mon mis­con­cep­tion that DNA evi­dence is wide­ly avail­able in all cas­es and cen­tral to exon­er­a­tions, but the real­i­ty is that DNA exon­er­a­tions in death penal­ty cas­es are rel­a­tive­ly rare. DPI has iden­ti­fied 34 cas­es across 15 US states in the mod­ern death penal­ty era of peo­ple who have been exon­er­at­ed from death row with DNA evi­dence — with the first case being Kirk Bloodsworth in 1993 (he was con­vict­ed in 1985). These num­bers rep­re­sent just 17% of the 200 death row exonerations. 

The aver­age time spent on death row by peo­ple exon­er­at­ed thanks to DNA is 18.6 years, for a total across the 24 cas­es of 631 years spent in prison for crimes they did not com­mit. Few of these exonerees have been adequately compensated. 

The Innocence Project reports 375 DNA exon­er­a­tions in crim­i­nal cas­es between 1989 and 2020. Before 2000, only a hand­ful of states allowed post-con­vic­tion DNA test­ing. That changed in 2004 with the pas­sage of the Justice for All Act. In her 2020 arti­cle, Chi-Hsin Engelhart argues that post-con­vic­tion DNA test­ing is a pro­ce­dur­al due process right that should be con­sti­tu­tion­al­ly pro­tect­ed. She notes this pro­tec­tion is espe­cial­ly impor­tant in the con­text of death row to explore the poten­tial of wrong­ful exe­cu­tion, con­clud­ing that a denial of access and test­ing could lead to a vio­la­tion of the Eighth Amendment. Ms. Engelhart argues that courts should shift their empha­sis from final­i­ty to accu­ra­cy in the legal sys­tem, and that allow­ing for DNA test­ing in post-con­vic­tion pro­ceed­ings would advance this goal.

During a recent dis­cus­sion mod­er­at­ed by DPI Executive Director Robin Maher at the French Ambassador’s Residence in Washington, D.C., Vanessa Potkin, Director of Special Litigation at the Innocence Project, not­ed that DNA evi­dence is avail­able in less than 10% of crimes. The case of Marcellus ​“Khaliifah” Williams, who was exe­cut­ed on September 24, 2024, illus­trates that even when DNA evi­dence can be obtained from the crime scene, foren­sic mate­ri­als may degrade or become con­t­a­m­i­nat­ed, ren­der­ing them unus­able for prov­ing a defendant’s innocence. 

Robert DuBoise was wrong­ful­ly con­vict­ed of mur­der and sen­tenced to death in Florida in 1983 based on faulty foren­sics, includ­ing the since-debunked prac­tice of bite mark match­ing. DNA test­ing ulti­mate­ly exon­er­at­ed him in 2020 and in February 2024, Mr. DuBoise received $14 mil­lion com­pen­sa­tion for his wrongful conviction. 

As sci­en­tif­ic and tech­no­log­i­cal progress con­tin­ues, many pris­on­ers may ben­e­fit from these advance­ments. However, many legal pro­ce­dur­al bar­ri­ers con­tin­ue to block pris­on­ers from access­ing DNA evi­dence that has the poten­tial to exonerate them.