Saleh S.,18, was sentenced to eight years in youth detention by a court in Hanover on Thursday after he attempted to set fire to a shopping centre in the capital of Lower Saxony last year.
The teenager admitted to the court that he had thrown two Molotov cocktails into a shopping mall on February 5th 2016.
According to his own account, the teen wanted to kill as many people as possible, a court spokesman said. No one was injured in the attack
Saleh S. is the older brother of 16-year-old Safia S., who was convicted of attempted murder in January and sentenced to six years in jail.
The teenage girl stabbed and severely wounded a 34-year-old police officer, reportedly as ordered by Isis, though the terrorist group did not claim the attack.
Safia S. had admitted to the attack and apologized to the officer while first in custody, as well as during the trial.
According to investigators, Safia S.'s attack was the first Isis assault in Germany.
The brother and sister are the children of a German father and a Moroccan mother. The couple split up when the children were young. According to their father, the mother brought them up with strict religious values. Photos have been found showing a young Safia in the company of radical preacher Pierre Vogel.