Police in Northern Ireland suspect current members of the Provisional IRA of involvement in the murder of a father-of-nine in Belfast.
Detectives have said they are not in a position to assess whether the killing of former IRA member Kevin McGuigan was ordered by a command structure within the outlawed and supposedly defunct organisation.
Mr McGuigan was gunned down in east Belfast in a suspected feud between former IRA members last week.
Organisational involvement of the PIRA, if proved, would have major significance for the political process in Northern Ireland. It is almost 20 years since the group called a ceasefire.
Police Service of Northern Ireland Detective Superintendent Kevin Geddes said: "A major line of enquiry for this investigation is that members of the Provisional IRA were involved in this murder."
Mr McGuigan, 53, was shot dead in front of his wife Dolores outside their home in Comber Court in the republican Short Strand last Wednesday.
Mr McGuigan was suspected by some in the republican movement of involvement in the murder of former IRA leader Gerard "Jock" Davison in the nearby Markets area of Belfast three months ago.
There has been widespread speculation that his killing was a revenge attack by Mr Davison's one-time republican associates.
Detectives investigating the McGuigan murder have made a number of arrests and have charged a 53-year-old man with possession of a weapon with intent to endanger life. The accused - Patrick John Fitzpatrick from Lagmore Dale in west Belfast - was remanded in custody at Lisburn Magistrates' Court today.
Mr Geddes said police were investigating whether a criminal group calling itself "Action Against Drugs" was behind the killing.
He noted that the group had issued a public statement earlier this month threatening to "execute" anyone it believed was involved in the Davison murder.
"We have a main line of enquiry that Kevin McGuigan was murdered by members of Action Against Drugs in what they believe to have been in revenge for the murder of Jock Davison," he said.
Mr Geddes said while Action Against Drugs was made up of "criminals, violent dissident republicans and former members of PIRA" he said current members of the PIRA are also suspected of involvement in the murder. But he insisted Action Against Drugs was a "separate" organisation from the PIRA.
When asked directly whether members of the IRA or "former" members were involved, Mr Geddes said: "It is my assessment at this stage and my belief that people who are members of the Provisional IRA were involved in this murder, but we will not speculate on at what level."
In regard to the extent of PIRA involvement, he said: "I have no information at this stage to say whether this was sanctioned at command level or not and I am not prepared to speculate on that."
The IRA has been on ceasefire since 1997 and decommissioned its weapons in 2005.
Those steps were crucial pre-conditions of the political agreements that have brought powersharing to Northern Ireland.
Last week, First Minister and Democratic Unionist leader Peter Robinson warned Sinn Fein it will face expulsion from the Stormont Executive if IRA involvement in the McGuigan murder was proved.
However, Sinn Fein has vehemently rejected the suggestion the IRA had a role in the killing.
After the PSNI announcement, Sinn Fein Deputy First Minister Martin McGuinness tweeted: "The people who murdered Jock Davison are criminals. Those who murdered Kevin McGuigan are also criminals. They must be brought to justice."