Earlier this week, the Supreme Court denied a request for stay of execution in the case of Daniel Anthony Lucas. He was the fifth person executed by the State of Georgia in less than three months. His execution comes directly after that of Kenneth Fults, who was executed despite having an IQ in the intellectual disability range and a juror “who later called him a n****r.”

Lucas, along with his co-defendant Brandon Rhode, was convicted of a triple homicide during a burglary in 1998. Both men were only 18 years old at the time of the crime. In petitioning the Supreme Court for a stay of execution, Lucas’s attorneys argued that offenders under age 21 at the time of their crimes should not be sentenced to death if their crimes reflect “unfortunate yet transient immaturity” instead of “permanent incorrigibility.”

His attorneys cited opinions involving juveniles in both the death penalty and life without parole contexts in support of the argument. Roper v. Simmons categorically barred offenders under 18 from capital punishment, and Miller v. Alabama categorically barred offenders under 18 from mandatory life without parole sentences. Both opinions are concerned with how juveniles are categorically different than adults in their ability to control compulsive behavior due to brain development. Recent developments in neuroscience have demonstrated that the development of the brain to maturity continues up to the early-to-mid 20s. The ability to make reasoned judgments while emotionally stimulated is not completed until around age 25.

Many European nations have already recognized this difference between young adults and older, fully mature adults, instituting the protections for persons ranging from age 18 up to age 25. For instance, in Germany, offenders aged 18-21 are automatically initially processed in the juvenile courts. Section 105(1) No. 1 of the Juvenile Law permits trying a young adult as a juvenile when the offender’s “moral and psychological development was like a juvenile.” Sweden uses youth as a “distinct factor” by which “any statutory minimum sentence may be disregarded,” if the offender is under 21. Switzerland permits treating young adults as juveniles in the criminal justice system until age 25.

Lucas’s age would have presumably saved him from capital punishment in any of these countries, if they still used the death penalty at all. Additionally, the Supreme Federal Court in Germany held that “a young adult has the maturity of a juvenile if his or her personality is still developing.” Due to Lucas’s traumatic childhood, marked by exposure to extreme violence and drug addiction, as well as his addiction to drugs by age 12, Lucas’s psychosocial development at 18 years old was markedly lower than that of other persons of the same age.

While the Supreme Court sadly rejected Lucas’s petition, this is not the last time the court will see arguments that young adult offenders, whose brains are still developing, deserve greater protection from our harshest criminal punishments.