When a large car bomb exploded at Oslo's central government building last summer, killing eight and injuring more than 200, police first thought they were dealing with two bombers who were about to mount new attacks in the capital.
But while confusion reigned, Anders Behring Breivik was already driving by himself toward a Labour Party summer camp 40 km (25 miles) away, where he would massacre 69 people.
There was a possibility that more bombs had been positioned and also that more offenders could be active, police superintendent Thor Langli said on Tuesday, the seventh day of anti-Islam fanatic Breivik's trial.
For a period, we actually believed we were dealing with two perpetrators.
Until Tuesday, Breivik had been the trial's main witness, detailing coldly how and why he went about the July 22 attacks that killed 77 people in all.
He denied criminal guilt, saying his targets were traitors whose supposed embrace of multiculturalism and immigration was opening Europe to a slow-motion Muslim takeover.
Breivik followed intently as Langli described the Oslo blast site and the police response.
The main reason he suspected two attackers, Langli said, was that he heard conflicting descriptions of a man seen leaving the car that blew up.
He said a security officer who had reviewed a surveillance recording told police that the man was dark-skinned.
He described him as not Nordic (and) not African, but in between, Langli said.
Separately, he said, a fire official who saw the event from across the street said the man was light-skinned. Breivik is indeed light-skinned and was wearing a fake police uniform with a dark helmet and visor.
The police did not publicise the descriptions while the confusion reigned, but many commentators initially assumed the attack had been the work of al Qaeda or another Islamist group.
Police forensics experts said on Tuesday that most of those killed were blown to pieces. The nearest was a 32-year Ministry of Justice lawyer named Jon Vegard Lervaag.
One cannot conceive that Lervaag ever knew there had been an explosion, forensic technician Arne Stray-Pedersen said.
Ahead of the trial, which is expected to last 10 weeks, one court-appointed team of psychiatrists concluded that Breivik was psychotic while a second found him mentally capable.
(Reporting by Oslo newsroom)