A Norwegian customs official said Breivik's name was spotted by the Global Shield Program four months before the July bombing and shooting spree that killed 77 people.
His name came up after he bought chemicals from a company in Poland.
The official said the information was given to Norway's security police, PST in March. PST confirmed the transaction was legal and that there wasn't enough information to warrant further investigation.
Breivik has admitted he was behind the bombing outside the government headquarters in Oslo and the shooting spree at a summer camp on Utoya island. His lawyer has said Breivik denies criminal responsibility, saying he's in a state of war.
In a manifesto released just before the attacks, Breivik describes ordering sodium nitrate and aluminum powder from a Polish company, as well as other chemicals that can be used in explosives from other suppliers.
Investigators have said Breivik's low-key and law-abiding lifestyle before the attacks made it difficult to pinpoint him as a potential threat. They say he kept his plans to himself, and have found no evidence to support his claims of being part of a network with other militant cells.
The Associated Press contributed to this report.