"It's a matter of severe violence and hazing," a source told the Aftonbladet newspaper.
The five students from Sigtuna Humanistiska läroverk (SSHL) located north of Stockholm are between 17- and 19-years-old, and are now the subject of a preliminary criminal investigation, police confirmed for the TT news agency.
The five have allegedly been engaged in a long-running bullying campaign against a fellow student involving violence which prosecutor Yngve Rydberg compared with aggravated assault.
"Unfortunately, I can't say more because it could compromise the investigation. A number of people will be questioned," Rydberg told Aftonbladet
The head of the school, Kent Edberg, also confirmed the students had been arrested, but refused to provide any more details about the incident.
"Due to privacy concerns and out of consideration for all our students I can't comment any further on this," he told TT.
Edberg emphasized that he considered the matter an isolated incident at the school, adding that it was the school who notified police about the alleged assault.
"A crime at SSHL should be treated like a crime in society. When we receive indications about something that we can't handle within our regulatory framework, we report it to police," he said.
Edberg referred to the incident as "tragic" and said the school was still exploring what other measures to take to address the situation.
Late in 2011, Sweden's Schools Inspectorate (Skolinspektionen) slammed all three of Sweden's boarding schools – Sigtuna, Gränna and Lundsberg – over the schools' policies and attitudes toward hazing.
In March, a lawsuit seeking 178,400 kronor ($26,523) in damages was filed against Lundsberg on behalf of a former student who had suffered continuous bullying at the hands of other students.
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Sigtuna Humanistiska läroverk was formed in 1980 through a merger of Sigtunastiftelsens Humanistiska Läroverk and Sigtunaskolan and currently has an enrollment of about 580 students, two thirds of whom live at the school.