Anders Breivik has been on a Norwegian security service watch list since March according to reports in the country.
Newspaper VG Nett reports that the killer was put on a list after reportedly buying large amounts of fertiliser from an online shop in Poland.
His name was among 60 passed to the Police Security Service (PST) by Norwegian Customs as having used the store to buy products.
But the flag was considered not to be relevant by the PST as he was thought to have been buying the chemicals to use on his farm.
Breivik then used the fertiliser to construct a bomb which killed eight in Oslo, before going on a gun rampage on Utoya Island, murdering 68.
Speaking to the newspaper, Jon Fitje of PST said the information they found gave no indication of anything suspicious.
He said: "There was no information that gave rise to anything. We had no indications that he had any plans for terrorist attacks."
Despite this, the security services in Norway still accessed his phone and email.
However they only did this for 24 hours because they had no suspicion basis on which to examine Breivik's actions further.
The security service also considered that Breivik's life "had been extremely law-abiding" according to PST director Janne Kristiansen.
Kritstiansen said: "He may possibly have had some traffic offences, but he has deliberately put his life in order not to get attention.
"He has also deliberately failed to be violent in statements online, not been a part of any extremist network and had registered guns, but was a member of a gun club.
"It is remarkable that he managed to comply for so long.
"Everything he did (prior to Friday), he did for a legitimate reason. There had been no warning lights."
The lack of intelligence into Breivik shows the meticulous planning he put into every aspect of the atrocity.
It is now thought that Breivik's farm, located in the town of Ostre Asta, acted as a cover for his devastating attack, with his crops of vegetables, melons, roots and tubers allowing him to purchase plenty of fertiliser without arousing suspicion.
He is thought to have purchased around six tons of the chemicals just two months ago, with a spokesman for one company suggesting he was just like any other customer.
"He contacted us in the normal manner, ordered fertiliser and had it delivered," the spokesman said.
However he was actually using the farm to meticulously plan the attacks on Oslo city centre and Utoya Island and write his 1,500 page manifesto.
Detailed in its pages he describes his first experiments with the fertiliser nitrate explosives before detailing a successful test detonation at a remote location on June 13.
And on Friday afternoon he placed the bomb in a Volkswagen Crafter car close to the offices of the Norwegian Prime Minister and other key governmental buildings.
Its detonation caused the deaths of eight people, and caused serious injuries to 15 more. The Prime Minister of Norway, Jens Stoltenberg, was unharmed in the attack.
The death toll was considered to be less than it could have been as the attack took place in July, a popular holiday month for Norwegians.