Detectives investigating the horrific murder of a 15-month-old baby believe she may also have been the victim of a serious sex attack, the Belfast Telegraph understands.

Distressing details have begun to emerge about the final hours of Millie Martin, who died suffering from horrendous injuries including a broken back. As her grief-stricken family mourned the loss of a “beautiful and precious little girl”, police in Enniskillen questioned a 30-year-old man — understood to be Millie’s mother’s partner — over the harrowing death.

Police arrested the suspect on Friday after he went with Millie and her distraught mother Rachael Martin (25) to the Royal Victoria Hospital in Belfast where she had been rushed from the Erne Hospital in a critical condition.

Police and medical staff were said to have been “extremely shocked” by her condition.

While postmortem results have not been released, the tot is understood to have suffered from horrific injuries. It is understood that detectives are investigating the possibility Millie had been raped.

Neighbours spoke of a community deep in shock after it emerged that police are investigating claims the toddler had also been the victim of a serious sexual assault.

Police were last night given a further 24 hours to question a man — who is not the child’s father — about the murder.

Detectives arrested the 30-year-old suspect on Friday after he went with Millie and her distraught mother Rachael Martin (25) to the Royal Victoria Hospital in Belfast.

The baby was taken to casualty at the Erne Hospital on Thursday night after she was viciously attacked at her home in the Glebe Park area of Enniskillen.

She was later transferred to the Royal where she died from her horrendous injuries, thought to have included a broken back.

The Belfast Telegraph understands detectives are investigating the possibility Millie was raped.

A post-mortem has been carried out on tiny Millie’s body but the results have not yet been released. A PSNI spokeswoman said they were being withheld for “operational reasons”.

On Saturday, police were given another 36 hours to quiz the suspect by a court in Omagh.

The man in custody is believed to be the partner of Millie’s mother and a father-of-two from the Irvinestown area.

The BBC reported today that senior social workers within the Western Trust are helping police with their inquiry amid claims that the child was known to them.

It said social workers spent time over the weekend gathering notes and files on the case and sealing them for the police investigation.

In a death notice in today’s News Letter, Millie’s family said funeral details would be released later. The baby’s grandparents, Noel and Margaret Graham, have asked for donations to be made to the Royal Hospital for Sick Children in lieu of funeral flowers.

Millie’s heartbroken family released a poignant statement telling of their “unbearable grief” over her tragic death.

“The entire close-knit family are numb with pain — we simply can’t believe that our loving, darling little angel is gone,” it read.

“No words can describe the distress that we are going through right now. Millie was our beautiful and precious little girl and we feel blessed to have been able to share her short life.”

Tommy Gallagher, MLA for Fermanagh and South Tyrone, said it was “a horrendous incident”.

“Everyone is so shaken about what happened, they don’t want to talk about it,” he said. “I get the feeling that people will shiver when the full story comes out.”

Ulster Unionist councillor Bertie Kerr said Millie was “a lovely wee child”.

“I can’t understand the mentality of anyone behind such a heinous crime. It’s incomprehensible that this could have happened,” he said.

His party colleague Tom Elliot said police and nursing staff had been “extremely shocked” by the condition of the little child.