A grow­ing body of research into ado­les­cent brain devel­op­ment indi­cates that the brains of even those over the age of 18 con­tin­ue to phys­i­cal­ly change in ways relat­ed to cul­pa­bil­i­ty for crim­i­nal offens­es. The Supreme Court referred to such sci­en­tif­ic evi­dence regard­ing those under the age of 18 when it struck down the death penal­ty for juve­niles in 2005 (Roper v. Simmons) and when it recent­ly lim­it­ed life with­out parole sen­tences for juve­niles. According to Laurence Steinberg (pic­tured), a pro­fes­sor of psy­chol­o­gy at Temple University, the brain con­tin­ues a process called myeli­na­tion into a per­son­’s twen­ties. That process affects plan­ning ahead, weigh­ing risks and rewards, and mak­ing com­plex deci­sions. This research may yield mit­i­gat­ing evi­dence for younger defen­dants, includ­ing accused Boston marathon bomber Dzhokhar Tsarnaev. Steinberg’s research shows that some­one like Tsarnaev, who was 19 at the time of the bomb­ing, may not have the same under­stand­ing of his actions as an old­er adult would. Young adults are par­tic­u­lar­ly sus­cep­ti­ble to the influ­ence of peers. ​“What we know is that this is an age when peo­ple are hyper­sen­si­tive to what oth­er peo­ple think of them. It’s also an age when peo­ple are try­ing to fig­ure out who they are, and one way is by iden­ti­fy­ing with a group. There prob­a­bly are sim­i­lar­i­ties between the dynam­ics here and dynam­ics of anti­so­cial or delin­quent gangs. Older, more pow­er­ful young adults per­suad­ing younger ado­les­cents to do their bid­ding for them,” Steinberg said. 

(D. Goldstein, ​“The Teenage Brain of the Boston Bomber,” The Marshall Project, January 8, 2015). See Juveniles and Studies.

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