The teenager, whose identity was not revealed because he is a minor, allegedly told police he killed in fits of rage or out of revenge - or, in one case, because the victim wanted to date his sister, police inspector Enizaldo Jose Plentz said on Friday.

Police have enough evidence to prove that the unemployed high school dropout killed at least six people with an initial shot to the head before riddling their bodies with bullets, Inspector Plentz said. The authorities were still working to determine if he killed the other six. The teen was arrested last Wednesday.

'The news stunned everyone,' said hotel receptionist Salete Lanius in the teen's home city of Novo Hamburgo where the killings took place.

Mr Plentz said: 'During interrogation, he spoke with the frightening cold-bloodedness of someone who enjoys killing people.'

AP