Appearing with name and photograph, Högström, 34, said he was supposed to act as an intermediary to pick up the sign and sell it to a buyer, but in the end he wound up informing Polish police about the people behind the plot.
“I was asked if I wanted to take the sign from one location to another,” he told tabloid Aftonbladet.
“We had a person who was willing to pay several millions (of kronor, or hundreds of thousands of dollars) for the sign,” he said.
He claimed he helped police nab the people behind the December 18 theft.
Police recovered the five-metre metal sign — which means “Work Will Set You Free” in German — on December 20 in northern Poland and arrested the five Polish men.
The sign had been cut in three parts.
“I’m proud to have revealed everything,” Högström said.
Questioned by AFP after Högström made similar comments to the Swedish media under cover of anonymity, a Cracow police spokeswoman denied he played a role helping police catch the robbers.
“The phone call from Sweden came as we were already in the process of arresting the thieves,” she said.
Högström in 1994 founded the National Socialist Front, a Swedish neo-Nazi movement he headed for five years before quitting.
After leaving his party, he distanced himself from the movement and became a model citizen, joining an association called Exit which helps youths quit far-right movements, Aftonbladet claimed.
The National Socialist Front was dissolved in late 2008.
Polish prosecutors said on Wednesday they wanted to question three Swedish residents over the theft, without revealing their names, and have formally submitted a request to Swedish authorities for legal assistance.
The sign above Auschwitz’s gateway has long symbolised the horror of the camp, created by Nazi Germany in occupied Poland in 1940 and in operation until Soviet troops liberated it in 1945.