Christopher Robinson, 45, has been charged with the murder of prison officer Adrian Ismay, after having been previously charged with attempted murder, the Police Service of Northern Ireland has said.
Mr Ismay, who was a married father of three, was hurt after a dissident republican bomb detonated under his van on March 4 in east Belfast.
He suffered severe leg injuries and underwent surgery and was thought to be recovering but died suddenly on Tuesday.
Lawyers for the man accused of his murder have questioned the cause of his death and a second post-mortem examination will be carried out.
Solicitors representing Chris Robinson asked for a review of the medical care given to Mr Ismay in the 11 days between him suffering serious leg injuries and having a fatal heart attack.
The accused appeared at Belfast Magistrates' Court today to face the substituted charge.
During the hearing a police detective told the district judge he could connect Robinson with the charge, and outlined the preliminary post-mortem findings to the court.
"Mr Ismay died from pulmonary embolism due to deep vein thrombosis following explosion injuries to the legs," he said.
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A 52-year-old prison officer who was injured by a targeted booby-trap bomb blast in Northern Ireland earlier this month has died.
Married father-of-three Adrian Ismay was hurt after a dissident republican bomb detonated under the van he was driving to work on March 4 in east Belfast.
The prison officer was given surgery for severe leg injuries suffered in the attack and was thought to be recovering but died on Tuesday.
Police Service of Northern Ireland said it was "working to establish the exact cause of Adrian's death" while continuing to investigate the bombing, which a group calling themselves the New IRA has claimed to have carried out.
One man has so far been charged with attempted murder and causing an explosion with intent to endanger life.
Northern Ireland First Minister Arlene Foster tweeted her shock as reports of his death emerged:
I'm devastated. Can't believe the news. I was texting Adrian before we left for the US. He was doing well. My thoughts are with his family.
Prime Minister David Cameron and Northern Ireland Secretary Theresa Villiers also paid tribute.
Deeply saddened to hear prison officer injured in bomb attack in Belfast on 4 March has died. Thoughts with father-of-three’s family.
SofS: I am shocked & saddened to hear of the death of this prison officer. My thoughts & deepest condolences are with his family.
Chairman of the Prison Officers' Association Finlay Spratt said the death was a complete shock.
Mr Spratt said: "I have no doubt that the explosion that took place was a factor. He was not a person that I knew had any sickness or ailments.
"I just can't believe it. I was just ringing to find out how he was and that's the news I got."
Mr Spratt added: "He was out of hospital and for this to happen - it is as much of a shock as the attack itself."
The long-serving officer worked at Hydebank Wood Young Offenders Centre in south Belfast and had trained new recruits to the NI Prison Service.
The New IRA group told the BBC that Mr Ismay was targeted because he had trained guards at HMP Maghaberry.
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A group calling itself the New IRA has claimed responsibility for a Semtex bomb attack that injured a prison officer in Belfast, according to reports.
The 52-year-old, a married father of three, required surgery after an explosive device detonated under the van he was driving on Friday morning. His condition has been described as stable.
Four people including a woman have since been arrested.
In a statement to the BBC, the dissident republican group reportedly said the officer was targeted because he was involved in training other guards at HMP Maghaberry, near Lisburn.
A spokesman said the officer was one of a number on a list of potential targets and the attack arose from a dispute over the treatment of dissident Republican inmates.
The group claimed to have used the plastic explosive Semtex and a commercial detonator in the attack.
Police investigating the attempted murder of a prison officer in Belfast on 4 March have arrested three men and a woman, the Police Service of Northern Ireland has said.
Detectives investigating the attempted murder of a prison officer in Belfast on Friday, 4 March have arrested three men and one woman.
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A pensioner and a teenager who allegedly went joyriding in a fire engine before smashing into cars and houses have been charged with a string of offences in connection with the incident.
The men, aged 66 and 19, are alleged to have stolen the fire engine in the early hours of Saturday from a station in Larne, Northern Ireland.
The Police Service of Northern Ireland (PSNI) said the men, who have not been named, will appear at Coleraine Magistrates' Court on Monday to face charges including aggravated vehicle taking, burglary and "various other offences".
A PSNI spokeswoman said: "Detectives have charged a 66-year-old man with burglary, aggravated vehicle taking causing damage to another vehicle, aggravated vehicle taking causing damage to property and various other offences.
"Detectives have also charged a 19-year-old man with dangerous driving, burglary, attempted burglary with intent to steal, aggravated vehicle causing damage to another vehicle and aggravated vehicle taking causing damage to property and various other offences."