According to investigators, a knife attack on a school playground in Finnentrop with three injured was preceded by a long smoldering argument.
In the incident in the Sauerland city, three young people were injured, some seriously, on Monday.
A police spokesman said on Friday that there had been arguments between two groups for a long time.
Because of the young age of those involved, the investigators did not provide any details.
The two seriously injured are doing much better, the spokesman reported.
At least one of the two has been released from the hospital and has already been questioned by the police.
The police in the Olpe district did not comment on the content.
Some teachers and classmates were also interviewed.
Five students between the ages of 15 and 17 were involved in the dispute during a break from class.
One had drawn a knife.
Two directly involved and a presumed "mediator" were injured.
Two 17-year-old brothers were provisionally arrested as suspects.
The investigations by the police, the Siegen public prosecutor and the Hagen homicide squad continued.