Prison officer Adrian Ismay had worked alongside a man accused of bombing him within a voluntary organisation, it has emerged.
The 52-year-old died on Tuesday, 11 days after a republican bomb detonated under his van in Belfast.
Mr Ismay suffered leg injuries in the blast close to his east Belfast home on March 4 but had been well enough to leave hospital within days.
He suffered complications on Tuesday and died after being rushed back to hospital.
As well as his full-time role as a trainer of prison staff, Mr Ismay was a dedicated member of the Community Rescue Service (CRS).
He also made his expertise available to a number of other voluntary bodies – one of which he served in, and helped train, Christopher Alphonsos Robinson, who is on remand having been arrested two days after the attack.
On Wednesday the PSNI said: “Following the death of Adrian Ismay and subsequent post-mortem examination, detectives from Serious Crime Branch have today launched a murder investigation. The post-mortem concluded that Mr Ismay died as a direct result of the injuries sustained during the explosion.”
Robinson, from Aspen Park in the Twinbrook area of Dunmurry, has been charged with attempted murder and possessing an improvised explosive device with intent to endanger life.
As a result of the post-mortem results, it is expected the 45-year-old will now be charged with murder.
It has now emerged that the two men had been volunteering together prior to 2014.
NI Prison Service Benevolent Fund chairman Ian Simpson has spoken of the “very difficult situation” facing Mr Ismay’s family.
“Given Tuesday’s events, they are totally devastated,” he said.
“There isn’t really anything that anybody can say to change the situation, all we can do at this time is to give the family the help and the support and the love that they require to help them through this tremendously difficult time.
“Colleagues that have know Izzy over the 28, almost 29 years, that he completed in the Northern Ireland Prison Service are totally devastated that we have lost a wonderful friend, an excellent colleague and we affectionately called him the gentle giant.
“He was a larger than life character and he brought many a happy moment to us throughout the difficult past times in the prison service, and he was somebody that you would want to be around.”
Commenting on the continued threat to prison staff, Mr Simpson told UTV: “It is a very difficult time for the men and women of the Northern Ireland Prison Service, and we would simply say to all of our colleagues at this time is to keep themselves safe.”
Speaking on the Nolan television show on Wednesday night, Republican Sinn Fein president Des Dalton was asked to explain how the murder of Mr Ismay was going to advance any political cause – and if he was prepared to condemn the killing.
“Every death, every loss of life, is a tragedy,” he replied.
“It’s a tragedy for families, it’s a tragedy for wider society. I think every death diminishes us, including the death of this particular man. It diminishes all of us human beings as a society.
“Any of the deaths that we have suffered in this country, either north or south over the last decade, none of them lead us any farther, but we need to look at the political context, and the fact that the elephant in the room is that the issues that caused our conflict have not been addressed. As long as that is the case then the cycle isn’t being broken.”
Asked specifically if he could condemn the murder, Mr Dalton said: “I am not here to condone or condemn anything here tonight. I am here to make a political analysis on what’s happening in terms of the broader situation and where we are at the moment.”
Also speaking on the same programme, DUP MLA Paul Givan said he found Mr Dalton’s lack of condemnation “despicable”.
Mr Givan said: “I don’t know how anybody can sit here and not condemn taking the life of Adrian Ismay, and if you’re not in a position to condemn that death then you’re not in a position to be part of the future of Northern Ireland, and that’s how we as a society have to deal with the people responsible for this. I think that is a despicable place for you to be in and you should be ashamed of that.”
Following the programme being broadcast, the commentator Alex Kane tweeted: “The logic of Des Dalton is hideous and his so-called position is deeply, profoundly, fundamentally stupid.”
Victims’ campaigner Willie Frazer said the criticism levelled at Des Dalton was justified, but said Sinn Fein must also condemn past violence.
Mr Frazer said: “The glorification of a terrorist campaign will only lead to another in the future, that is why victims have always called for Sinn Fein/IRA to condemn their acts of violence in the past and that any violence can never be justified.”