Police have described the killing of a man in north Belfast as a "callous and cold-blooded murder".
Kevin Kearney's body was found in a lake in Alexandra Park on Wednesday afternoon. He had been shot.
Mr Kearney was 46 and a father of four, and lived at Dunmore Avenue close to the park, which is off the Antrim Road.
The Irish News reported that it received a statement from a dissident republican group calling itself "the IRA" that claimed it killed Mr Kearney.
In July 2012, a new paramilitary group styling itself "the IRA" is believed to have been formed from an amalgamation of previously disparate dissident republican organisations.
BBC NI Home Affairs Correspondent Vincent Kearney said: "CCTV cameras at the home of the father of four suggest he may have felt under threat, and local sources said he may have been involved in low level drug dealing."
Police Service of Northern Ireland (PSNI) Det Ch Insp Justyn Galloway said that Mr Kearney "was known to the police".
"Kevin was known to us for previous offending, but what I want to make clear is regardless of Kevin's lifestyle, regardless of his previous offending, there is no justification whatsoever for someone to shoot him dead as they did."
Mr Kearney left his daughter off at school on Tuesday morning, and returned home and took his dogs for a walk in Alexandra Park.
He was wearing dark clothing and distinctive bright blue trainers, and police say he was shot at approximately 09:15 BST on Tuesday.
He was reported missing on Tuesday evening when he had not returned home.
Police have appealed for information on a silver Peugeot 406 car, registration number GNZ 8168, that was found burnt out in Dunore Court in the New Lodge area of north Belfast at about 09:30 on Tuesday morning.
They also want to hear from anyone who was in the park between 08:30 and 09:30 on Tuesday.
DCI Galloway added: "We are aware of the claim of responsibility and that is forming part of my investigation and it is a line of inquiry.
"Kevin has been going about his normal routine so there is an element of targetting. He has been shot in a callous and brutal way.
"It is important that we identify witnesses, recover the firearm that was used, and we can only do that with the cooperation of the people of north Belfast, which I have to say to date has been fantastic."
Secretary of State Theresa Villiers condemned the murder and that of a man in Londonderry on Thursday. Police have said at this stage they are not the murders.
"The murders of two men in Londonderry and north Belfast are abhorrent and brutal crimes, for which there is no excuse," she said.
"I am sure the police will leave no stone unturned in bringing to justice the people responsible for these disgraceful attacks."
The murders were condemned by Deputy First Minister Martin McGuinness.
"Those responsible claim to be dissident republicans. They are not republicans of any shade. They are entirely motivated by criminal intent," he said.
DUP North Belfast MP Nigel Dodds said: "The entire community will share in the sense of shock at this appalling news.
"Our thoughts are with the family of the deceased. I appeal for anyone who can assist the police investigation to pass on whatever information they have."
Sinn Féin North Belfast MLA Gerry Kelly said: "The murder of Kevin Kearney is to be condemned outright. The pseudo 'republican' group that carried out the killing have no support whatsoever within the local community.
"In fact, it is common knowledge that they have within their ranks people who have taken backhanders from drug dealers so that they can continue peddling drugs. This makes them the same as the drug dealers who bring death and destruction to the community.
"Masquerading under the name republican does not stop people from seeing these groups for what they really are. I would call on anyone who has any information on this killing to bring it forward to the PSNI.
"The people of north Belfast have suffered enough throughout the years without the blight of these maverick, self-serving, hypocritical groups bringing death to the community."
SDLP councillor Pat Convery, who chairs the north Belfast community safety partnership, said: "This is a very tragic event.
"My thoughts and prayers are with the man's family."
The park has been closed to the public while the investigation continues.