Danielle Wails, 21, had told police that two masked men burst into her home, bound her and set light to the building before leaving her and her four-month-old son to burn to death behind locked doors. While she escaped with minor injuries, the baby, Alexander Gallon, could not be saved by the time firefighters broke down the door.
On Tuesday, Northumbria Police appealed for help in tracing the two men who had carried out what they called a "wicked" crime. But yesterday the force announced that a 21-year-old woman had been arrested. While refusing to confirm that the woman in custody was Ms Wails, an officer said: "We have suspended our appeal for those two men".
Ms Wails and her son had been living in the house in Cowgate, Newcastle upon Tyne, for just a few weeks. Run by the Catholic charity St Cuthbert's Care, it provides a home for young single mothers who need help with their parenting skills.
Neighbours said that they heard screams on Sunday night but could not get through the locked door. When firefighters arrived, Ms Wails emerged with binding on her hands, calling for her baby.
She said that the attackers had knocked her unconscious and by the time she had come round, she could not get to Alexander because of the intensity of the heat and was forced to dial 999 with her tongue because her hands were tied.
The baby was declared dead upon arrival at Newcastle General Hospital. Following a post-mortem examination carried out by the Home Office pathologist Dr James Sunter and the paediatric pathologist Dr Chris Wright, early indications showed the baby was killed by the fire though further tests are being carried out.
Another woman, who was said to be in her early twenties, was released on police bail on Tuesday after being questioned as part of the inquiry. Officers said yesterday that they wanted to speak to two men who had been in the area shortly before the fire broke out.
A force spokeswoman said: "We have CCTV footage that shows two men at the corner of Link Road and Whitehorn Crescent at 10.30pm on Sunday. We would ask for these two men to come forward and contact the incident room."
Ms Wails was released from hospital earlier this week and police said that she was being comforted by Alexander's father, Robert Gallon, also 21. Although the couple did not live together, he had remained close to his son. In the initial appeal, Detective Superintendent Barbara Franklin, who is leading the investigation, told a news conference: "It is difficult to comprehend the wickedness of someone who could do such a thing and we appeal for the public to come forward and help us."
Detectives and forensic officers remained at the house yesterday.