He was interviewed over a phone call he made to a suspect in the Karachi affair, to warn him that his estranged wife had been talking to investigators.
The call to Thierry Gaubert, who was also a close aide to Sarkozy before he became president, was intercepted by investigators and leaked to the media.
Gaubert's wife had told police that her husband made trips to Switzerland in the 1990s to collect suitcases full of cash to finance Edouard Balladur's unsuccessful presidential campaign.
Nicolas Sarkozy was campaign spokesman for Balladur at the time, and also budget minister.
It's alleged that the Swiss money was kickbacks from arms sales to Pakistan, and that a 2002 bombing in Karachi, which killed 11 French engineers, was revenge for the cancellation of bribes which had been secretly promised to Pakistani officials.
Hortefeux is accused of breaching the confidentiality of a judicial investigation, but he said after Friday's interview with police that he was able to demonstrate that he "knew nothing of the contents of the judicial investigation."
He was released without charge after three hours and issued a statement saying he had been questioned at his own request, as a witness.
Gaubert has already been charged and is under investigation.
Sarkozy insists he had no responsibility for the financing of Balladur's campaign, but the allegations surrounding many of his close friends and associates at the time, are adding to the current climate of sleaze just months ahead of his re-election bid.
In the recorded phonecall to his friend four days after Gaubert's estranged wife spoke to police, Brice Hortefeux says: "She's giving away a lot, apparently, Hélène".
"What news have you got on that?" Gaubert asks.
"I don't want to discuss this on the phone", Hortefeux replies, adding "There's a lot though, eh?"
"Hélène didn't speak to them directly," Gaubert insists, surprised.
"She was interviewed. She knows. She was aware of your activities. Listen, uh, try to drop by to see me one of these days anyway," suggests Hortefeux.