A Norwegian man suspected of setting off a blast that killed seven in central Oslo and gunning down 84 youths at a political meeting on Friday bought 6 tonnes of fertiliser in May, a farm supply firm said on Saturday.
Some kinds of agricultural fertiliser have been used in the past to make explosives.
The suspect, identified by Norwegian media as Anders Behring Breivik, placed the order through his company, the supplier said.
"These are goods that were delivered on May 4," Oddny Estenstad, a spokeswoman at agricultural supply chain Felleskjoepet Agri, told Reuters, without giving the exact type of fertiliser purchased.
"It was 6 tonnes of fertiliser, which is a small, normal order for a standard agricultural producer."
"I do not know him or the company, except that it is a company that has contacted us in a normal manner and ordered fertiliser and had it delivered," she said.