The 13-year-old in Sinsheim near Heidelberg was killed out of jealousy according to the investigators' initial findings.
The investigation into the motive continued, said Siegfried Kollmar of the Mannheim criminal police on Thursday.
A 14-year-old is suspected of having murdered the boy with multiple stab wounds, as Kollmar said.
How many stitches it was about, he didn't say.
One is still waiting for the written result of the autopsy, cell phones will be evaluated.
“We still have a lot to determine,” said Kollmar.
An arrest warrant was issued against the 14-year-old in the afternoon.
According to the chief public prosecutor, the suspect has not yet commented.
As Kollmar explained, according to the current status of the investigation, the 14-year-old lured the 13-year-old onto a dirt road.
Another child who was not of age was also there.
Kollmar did not want to comment on the person.
The alleged perpetrator is a boy who seriously injured a then 13-year-old with a knife at a secondary school in Östringen northeast of Karlsruhe last November.
At this point in time, the attacker was not yet of criminal age.
According to German law, young people between the ages of 14 and 17 are only “of limited criminal responsibility”.
The Lord Mayor of Sinsheim, Jörg Albrecht (independent), was dismayed by the act.
"The concern is great, that hits a place in the marrow," said the town hall chief.
In his nine years at the top of the city, he had never experienced anything like this.
The shock was also deep in the Eschelbach district, where the crime scene is located: Mayor Wolfgang Maier said that his phone had not stood still.
"People are worried, but I was able to defuse them."
The dead youth was found in a field on Wednesday afternoon.
The 14-year-old was arrested in the immediate vicinity of the site.
Even if such violent outbreaks are rare, they always cause a stir: In Duisburg, a then 14-year-old admitted last October that he had killed his girlfriend of the same age.
And in April of last year, a 17-year-old is said to have killed a 14-year-old in a dispute at a bus stop in Essen - the murder weapon was again a knife.