USA | Forensics, ​“Junk Science”, and the Death Penalty

Saturday April 25th is National DNA Day, mark­ing the anniver­sary of the 1953 dis­cov­ery of DNA’s dou­ble helix struc­ture and the 2003 com­ple­tion of the Human Genome Project. Today, the Death Penalty Information Center is pleased to present a new resource exam­in­ing the con­tro­ver­sial role of ​“junk sci­ence” in cap­i­tal cas­es. When DNA test­ing became one of the most rig­or­ous­ly val­i­dat­ed tools in foren­sic sci­ence, its devel­op­ment also prompt­ed greater scruti­ny of oth­er foren­sic tech­niques. Many dis­ci­plines that were long accept­ed in U.S. court­rooms have now been found to lack ade­quate sci­en­tif­ic foun­da­tion and have become known as ​“junk science.”

Of the 202 indi­vid­u­als list­ed on DPI’s Innocence List, 65 of these wrong­ful con­vic­tions and death sen­tences were based in part on junk sci­ence and flawed foren­sic evi­dence. Nearly 60% of these exonerees are peo­ple of col­or, and almost half are Black. The foren­sics used to con­vict these indi­vid­u­als includes arson inves­ti­ga­tion, bal­lis­tics and tool-mark analy­sis, bite mark com­par­i­son, micro­scop­ic hair analy­sis, and so called ​“Shaken Baby Syndrome” — tech­niques that most courts accept­ed for decades with­out ques­tion or rig­or­ous scientific scrutiny.

Our new resources com­pre­hen­sive­ly exam­ine each of these dis­ci­plines: the his­to­ry of their use, how their reli­a­bil­i­ty came to be ques­tioned, and how they have affect­ed cap­i­tal cas­es. Among the cas­es exam­ined is that of Cameron Todd Willingham, exe­cut­ed in Texas in 2004 based on arson evi­dence lat­er shown to be premised on out­dat­ed and invalid method­ol­o­gy. Also cov­ered is the FBI’s 2015 review of micro­scop­ic hair com­par­i­son tes­ti­mo­ny, which found that its expert wit­ness­es gave erro­neous tes­ti­mo­ny in 96% of cas­es reviewed — includ­ing nine cas­es in which pris­on­ers had already been exe­cut­ed. On bite mark com­par­i­son, no court has broad­ly ruled the evi­dence inad­mis­si­ble, yet bite mark evi­dence has con­tributed to more than two dozen wrong­ful con­vic­tions across the U.S., includ­ing cap­i­tal cas­es. Regarding bal­lis­tics and tool mark evi­dence, a 2023 Maryland court recent­ly ruled that a firearms exam­in­er had over­stepped sci­en­tif­ic bound­aries by tes­ti­fy­ing with ​“prac­ti­cal cer­tain­ty” that shell cas­ings matched a defendant’s firearm, a con­clu­sion that the court found lacked suf­fi­cient scientific foundation.

DPI’s new resource also doc­u­ments the evo­lu­tion of the legal system’s approach to foren­sic evi­dence. The U.S. Supreme Court’s Daubert deci­sion in 1993 estab­lished a new stan­dard for the admis­si­bil­i­ty of sci­en­tif­ic evi­dence, and a 2016 report from the President’s Council of Advisors on Science and Technology exam­ined the lim­i­ta­tions of sev­er­al long-accept­ed foren­sic tech­niques. A 2023 National Institute of Justice study found that sys­tem­at­ic errors across more than 30 foren­sic dis­ci­plines have con­tributed to wrong­ful con­vic­tions. Today’s courts increas­ing­ly rec­og­nize that sci­en­tif­ic knowl­edge is not sta­t­ic, and what con­sti­tutes ​“junk sci­ence” may con­tin­ue to change as under­stand­ing deep­ens, and ana­lyt­i­cal capabilities improve.

Learn more about these foren­sic dis­ci­plines at our Junk Science page.

Source: Death Penalty Information Center, Staff, April 24, 2026

"One is absolutely sickened, not by the crimes that the wicked have committed,
but by the punishments that the good have inflicted."

— Oscar Wilde

Death Penalty News For a World without the Death Penalty