ATHENS, Greece — Nine men arrested in the beating death of an American student outside a bar in Greece in 2017 were cleared of murder but convicted of assault charges on Thursday.

A court in Patra, in western Greece, reduced the charges to grievous assault, handing six men sentences ranging from five to 15 years in prison and freeing three others after convicting them of simple assault for the brutal attack on the student, Bakari Henderson, 22, in the summer of 2017 on the holiday island of Zakynthos.

The verdict disappointed the parents of Mr. Henderson, who have said that they were hoping all the men would be sentenced to life in prison. The prosecution attorney, Andreas Patsis, said that the outcome had “shattered” the relatives and that they did not think justice had been done.

The decision spurred Mr. Henderson’s parents to warn other Americans against allowing their children to visit Greece.