The dog named "Uno" that savaged and killed John Paul Massey, ripping his throat and head, was an banned American Pit Bull terrier.
Merseyside Police said that following extensive examinations and a post mortem an independent expert has confirmed that the dog was pit bull terrier type, which is classified as a dangerous dog under the Dangerous Dogs Act (1991).
A Merseyside Police spokesman said that further forensic tests on the dog are still being carried out and investigations into the attack are ongoing.
Merseyside Acting Deputy Chief Constable, Patricia Gallan, said: "Our thoughts remain with John Paul's family at this time following his tragic death.
"A child's life has been lost and it is essential that we determine the exact circumstances surrounding the attack.
"Investigations into the incident are continuing. Ascertaining the type of dog involved in this attack has been a complex issue.
"It has taken some time to complete the examinations and post mortem before we have been able to confirm that it is an illegal type of dog. We are conducting a criminal investigation.
"On behalf of Merseyside Police, I am deeply concerned and very disappointed that our policy was not followed in February when we received a call alerting us to the possible breeding of pit bull terriers at the house where the attack took place.
"This is clearly unacceptable and we are sorry that Merseyside Police did not take the appropriate course of action at that time.
"As a matter of urgency we began an immediate internal investigation to establish exactly what led to that call not being brought to the attention of our specialist dog unit.
"Given the seriousness of this situation, and our failure to follow our own procedure, we have referred this case to the Independent Police Complaints Commission who will be carrying out an independent investigation.
"We take the issue of dangerous dogs very seriously and there is no place for them on the streets of Merseyside. During the last three years we have taken action to take dangerous dogs off the streets.
"We are determined to continue our work to ensure the safety of people living, working and visiting Merseyside. I would urge anyone who has concerns about a dangerous dog to contact us."
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