The ghost of Jean McConville is one that comes back time and time again to haunt the career of Gerry Adams.
Abducted, shot, and buried like a dog in Shelling Hill Beach, Co Louth – where the Sinn Féin president is now a TD – the murder of the widowed mother of ten hovers over the political landscape.
The death of a woman, who at the time of her murder in December 1972 republicans regarded as insignificant, has refused to go away. The IRA believed she was an informer saying they recovered a radio from her home which she used to communicate with the British Army. Her family strongly deny the claim.
Gerry Adams has long denied he was involved in her murder. He told the McConville family that he was in jail at the time of their mother's death – which he was not.
Were it merely police sources blaming him for the McConville murder, he would be on safe ground. The retort that it was just "the securocrats" up to no good would strike a chord with the nationalist community.
But it is the testimony of republicans, of fellow IRA men and women who were once Gerry Adams' closest comrades, that makes the case connecting him to the murder so powerful.
Brendan Hughes, a former IRA Belfast Brigade commander, was once Gerry's Adam's best friend. "I loved him. I'd have taken a bullet for Gerry. I probably should have put one in him," said Hughes, sickened by the hypocrisy and the Sinn Féin president's insistence he'd never even been in the IRA.
Hughes died six years ago but in a taped interview with oral history researchers from Boston College, he challenged Adams' narrative. "I never carried out a major operation without the OK or the order from Gerry," he said.
"This woman was taken away and executed. .. . Jean McConville. There was only one man who gave the order for that woman to be executed. That man is now the head of Sinn Féin and he went to this family's house and promised an investigation into the woman's disappearance.
"That man is the man that gave the order for that woman to be executed. I did not give the order to execute that woman – he did."
Hughes' claim was supported by Dolours Price who along with her sister Marian bombed the Old Bailey in 1973. Price died last year but in a taped interview before her death she admitted to having driven McConville from Belfast to her fate across the Border. She said she had taken her orders from Gerry Adams.
It is also understood that other taped interviews in the Boston College archive, which were handed over to the PSNI last year after a lengthy legal battle, implicate Adams.
However, while this has led to Adams being arrested and interviewed under caution, it seems unlikely to be strong enough to have him charged and prosecuted with murder. Hughes and Price are dead so they cannot be called as witnesses to corroborate their claims on tape.
It is highly unlikely that other republicans who are still alive and have supported the claims of Hughes and Price on Adams role in the murder would agree to be witnesses against the Sinn Féin president.
No matter how much their desire that the truth be told about Adams and no matter how they now hate him, their antipathy about giving evidence in a British court – "turning tout" as it would be seen in republican circles – is greater.
Given that Jean McConville lay buried in Shelling Hill beach for decades, it is hard to envisage valuable forensic evidence having been recovered from her body.
And any DNA evidence that would possibly be found would be that of those who walked her to the beach and shot her, and not that of the person who gave the order many miles away in Belfast.
The bitterness in republican circles over the Sinn Féin president's constant denial of his IRA career means that there will be as many republicans privately pleased about his arrest as there are unionists.
But the arrest of Gerry Adams shouldn't lead his opponents to believe that this necessarily marks the beginning of the end for him. Apart from a brief period of internment, unlike so many IRA members he escaped life behind bars and it's difficult to imagine that's going to change now.
He had spectacular luck during the conflict. It's hard to believe that he won't survive this just as he has survived so much before. The timing for Sinn Féin is bad. To have their leader arrested and questioned about the murder of a widowed mother of ten weeks before the elections isn't good PR.
The ghost of Jean McConville still hovers stubbornly but it's unlikely to be ever laid to rest by the reality of securing justice.