THE CHIEF suspect in garda custody over the murder of Helen Donegan will be charged in relation to her killing by tomorrow night.

The 45-year-old man has admitted to shooting the mother of one, but has claimed it was accidental, it is understood.

Detectives are due to return to court tonight to have his period of detention extended for a final 24 hours.

The man was well-known to Donegan. He has been in garda custody since Tuesday when her body was discovered in the boot of a car in Clondalkin, Dublin. She had been shot dead and had been missing since 6 May.

The 30-year-old mother, who was addicted to crack cocaine and worked as a prostitute, has a 12-year-old son who lives with his grandmother in Co Clare.

The man in custody has told detectives that he got involved in a row with her over her drug habit. He has claimed she tried to grab the shotgun he was holding, which went off accidentally as a result, and she was shot once in the chest, killing her. 

The 45-year-old has told detectives he was trying to get Donegan off crack cocaine; she was spending €150 a day on the habit and working as a prostitute to earn money. The man is custody has no previous convictions and is considered an "ordinary Joe Soap" by detectives.

"It seems to be a bit of a tragic story for everyone involved. The fact that he concealed and moved her body around certainly raises several questions about his story," said a source.

Helen Donegan was last seen at her home at St Patrick's Park, Celbridge, Co Kildare on 6 May. Gardaí feared for her safety from the time she was reported missing by her partner and had carried out searches.

On Tuesday evening, they searched a lock-up in a transport yard at Kilmactalway, Aylmer Road, just outside Newcastle in Co Dublin. Gardaí found Donegan's badly decomposed body in the boot of a silver-grey Saab estate. A post-mortem revealed she had been shot once in the chest. Her remains were so badly decomposed that DNA tests and dental records were used to identify her.

Gardaí believe she was killed about the time she was reported missing, and that her remains were put into the boot of a blue Seat estate, which was stored in a garage in Co Kildare for some weeks. When the owner of the garage returned, her killer moved the remains. Her body was then placed in the boot of the Saab, which was locked away in a second unit in Co Kildare. The murder weapon, a legally-held shotgun, was handed into gardaí shortly after she went missing.

Gardaí had suspicions that the man in custody was involved in her disappearance immediately after Donegan went missing. Detectives say ballistic tests, which will determine whether the gunman shot her while standing above her at a height, or at the same level – will be crucial. The fact that her killer concealed and moved her body between two cars is another factor to be considered by the DPP in whether he will be charged with murder or manslaughter.

Donegan is originally from Ballyfermot in Dublin. The 45-year-old in custody is being held at Clondalkin garda station.