Police have arrested a second person in relation to the death of a three-year-old boy in July.
Following on from the arrest of 27-year-old woman on Thursday morning, detectives from the PSNI serious crime branch have detained a 51-year-old man.
Police said the boy - named as Brendan Owens - was found dead in Lisburn, Co Antrim, on July 4.
A spokeswoman said: “Detectives are now treating this as a murder investigation.
“The woman remains in custody at this stage, helping police with their inquiries. There are no further details available.”
Brendan’s body was found at Trinity Terrace, close to the centre of the city.
At the time of his death, neighbours said residents of the newly refurbished terrace house, close to Holy Trinity nursery school, had moved into the busy side street just a few months before the death.