Mr O'Hagan was shot yards from his Lurgan home
Martin O'Hagan, 51, was shot dead in Lurgan, County Armagh, as he walked home from his local pub.
The Red Hand Defenders, a cover name used in the past by both the Loyalist Volunteer Force and the Ulster Defence Association, said it carried out the killing.
The weapon used to kill the father-of-three was understood to have been linked to a previous LVF shooting.
Security Minister Jane Kennedy made her comments about the murder investigation to a delegation from the National Union of Journalists at Stormont on Tuesday.
She said: "I too want to see the people who carried this out brought swiftly to justice".
The NUJ, which sought the meeting to discuss the progress of the investigation and other issues surrounding the security of journalists, welcomed the minister's comments.
But NUJ general secretary Jeremy Dear said the union would be pressing for further action by the Police Service of Northern Ireland.
"If action is not taken to ensure the security of individual journalists at risk and the wider general threat to journalists, there is a real danger of self-censorship undermining the media's critical role in keeping the public informed," he said.
Irish secretary Eoin Ronayne said the meeting was the "opening move in a campaign to support investigative journalism and individual journalists under threat".
He said he would be seeking a follow up meeting with the chief constable.
He also said the union was determined that the murder of Mr O'Hagan would not stop journalists from doing their work.
Bosses
Mr O'Hagan worked in the Belfast office of the Dublin-based Sunday World, where he built a reputation covering paramilitary and drugs-related stories.
He infuriated County Armagh paramilitary bosses, including murdered LVF leader Billy Wright, by exposing their crime and drugs rackets.
Mr O'Hagan had been working on a number of stories involving LVF members shortly before his death.
After the killing, the then chief constable, Sir Ronnie Flanagan, said that police inquiries were concentrating on the LVF.
It is understood the police have established the same gun was used in the killing of a Tandragee man earlier that year, in a murder thought to have been carried out by the LVF.