The authorities had originally claimed that no excess violence had been used by the guards on the boy, but following new complaints from the public, the police say they will once again open the case, Swedish Radio in Malmö reports.
Police claim two boys were on the run from a children's home and posed a danger to themselves and others, but the actions of the guards against one of the boys have caused a storm in social media in Sweden.
One of the security guards has reported one of the boys for violent behaviour, but the investigation was dropped due to the boy's young age, newspaper Sydsvenskan reported.
Radio Sweden interviewed legal expert Sven-Erik Alhem, who has worked as a chief prosecutor in Malmö and Stockholm, who criticized the police for not opening an investigation immediately.
Two demonstrations against the actions of the guard are planned this evening in Malmö and Stockholm.