The boy was found under a bush last week after his parents reported him missing when he failed to return to his home in the northern town of Pragsdorf.
Although rescuers tried to revive him, he died later in hospital.
Investigators found a knife near the crime scene that is believed to have been the murder weapon.
Police have now linked DNA traces found on the knife to a 14-year-old boy, they said on Tuesday.
The teen had already been questioned because he was the last person to see the boy alive and had raised suspicions by making contradictory statements, the police said.
The case is the latest in a spate of murders involving minors in Germany this year.
Earlier this month, investigators concluded that two girls aged 12 and 13 had stabbed to death another schoolgirl near the town of Freudenberg, in the western state of North Rhine-Westphalia.
READ ALSO: German schoolgirls confess to fatal stabbing of 12-year-old
The victim, also 12, was found in March with multiple knife wounds in a wooded area not far from her home.
The two girls aged 12 and 13 had subsequently confessed to the murder.
Also this month, investigators concluded that an 11-year-old boy had murdered a 10-year-old girl at a children's care home in Wunsiedel, in the Bavaria region.
In August, a 15-year-old boy was sentenced to ten years' detention for murdering another boy of the same age several months previously in a game that turned violent in Wunstorf, near Hanover.
In Germany, the age of criminal responsibility starts at 14.
Comments