A picture of the dog believed to have killed a 10-year-old boy has been revealed.
Jack Lis was mauled to death at the home of a friend in Pentwyn, Penyrheol, Wales, on Monday.
The dog was shot by firearms officers who attended the scene.
Gwent Police confirmed on Wednesday they had arrested a woman on suspicion of being in charge of a dog dangerously out of control, causing injury resulting in death.
She has been released on conditional bail, the force said.
Watch: Detectives probe whether dog that killed boy was illegal
The dog was described as an "American bulldog or a pitbull" by neighbours, but this has not been confirmed and experts will examine it to check if it is an illegal breed.
Tests could be carried out to check the animal's DNA along with its owners and breeders being questioned by officers.
Chief Superintendent Mark Hobrough said experts will "look at the character traits of the dog" to see if it is a banned breed.
He said: "As our investigation continues, we will be removing our scenes from the area and the work to identify the breed of dog involved is also progressing.
“As we’ve arrested an individual on suspicion of an offence linked to the attack, and spoken to two others voluntarily, we’re looking to identify where any criminal matters have occurred.”
Jack and his friend were alone when the attack happened.
His friend sought the help of a neighbour who lived several doors down on the same street, but the man was unable to stop the dog.
Paramedics arrived at the scene just before 4pm but they were unable to save Jack.
Jack’s mother Emma Whitfield paid tribute to him on Facebook, writing: ‘With so much heart break […] I have to announce our beautiful boy Jack was taken so tragically yesterday.
‘It was not our dog nor did it happen at our family home. He was out to play.
‘We love you so much our sweet sweet boy.’
Two men voluntarily attended the police station in relation to the offence.
The 34-year-old from the Mountain Ash area and 19-year-old from the Caerphilly area were both later released.
Chief Superintendent Hobrough added: “I understand that there is a lot of interest about this in our communities.
“It is vital that people are considering the tone and language used in comment posted on social media about the identities of anyone involved in this matter as part of our enquiries.
“As this is a live investigation such comments may have impact on our ability to bring anyone found to have committed a criminal offence to justice.”
Anyone with information is urged to contact Gwent Police.
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