Not sure yet

News of two car explosions rapidly following each other in central Stockholm. One person dead and two injured. The way the dead one is described raises the probability that it may well have been somebody actually in one of the cars, which contained gas cylinders. Waiting for further news.

UPDATE: There were earlier rumours but the Guardian goes for it:

A Swedish news agency said it had received an email warning, ahead of the explosions, in which a threat made against Sweden and its population was linked to the country's military presence in Afghanistan.

The TT agency said the warning, which comprised sound files in Swedish and Arabic, was also sent to Sweden's security police (SAPO) and was received 10 minutes before the blasts.

It also referred to caricatures of the prophet Mohammed by Swedish artist Lars Vilks, who became the subject of death threats and at least one assassination plot after cartoons appeared in a Danish newspaper.

It definitely looks like one of the perpetrators is the dead body.