The boy, reported by Expressen to be 8 years old, was said by witnesses to have been stabbed several times.
The man is said to have started arguing with the boy. He then hit him, before pushing him to the ground and subjecting him to a knife attack.
The man was said to have then stopped attacking him for a while, then continued stabbing the boy until he died. He then left the scene.
At a press conference on Thursday afternoon police described the attack as “random”, adding that there did not appear to be any relationship between the boy and his attacker.
“The perpetrator is known to the police. He was sentenced to psychiatric care in 2004 for arson. He was released from psychiatric hospital on 27th November 2006,” said police investigator Lennart Wernblom.
“Our technicians have secured traces from the perpetrator. His apartment has been sealed off pending an investigation,” he added.
Police did not wish to reveal whether they had found the murder weapon.
Police in the county of Östergötland have noted similarities between Thursday’s murder and a double murder in Linköping in October 2004, when an eight-year-old boy and a 56-year-old women were stabbed to death by an unknown attacker.
“This is very similar, according to the information I have received,” said Benniet Henricsson, an investigator involved in the hunt for the double murderer.
He was informed of Thursday’s murder by police in Jönköping shortly after the attack took place.
“We are going to make sure that DNA tests are carried out as soon as possible on the man arrested today to see if we can find out if it was the same person we are looking for,” said Henricsson.