A 10-year-old boy was injured when he was bitten by a police dog in his grandmother's back garden.
Tom Cutbill was hurt in New Henry Street, Oldbury, while West Midlands Police officers responded to reports of a nearby copper cable theft, on Sunday.
A dog handler and his German Shepherd-Belgian Malinois cross were searching for four suspects when they entered a private garden and the boy was bitten.
West Midlands Police said it would carry out its own investigation.
The boy's family said he had undergone two operations since the attack.
Tom's father, Martin Cutbill, 40, said his son had bite wounds to his right leg, but he was now out of hospital and walking using crutches.
Mr Cutbill, of Rowley Regis, said: "There were quite a few puncture wounds and tears to the skin.
"He's had two operations, one to clean up the wounds to stop the risk of infection and the other one to seal the wounds."
Following an independent assessment, the dog handler and the dog continue to carry out regular duties, the force said.
The Independent Police Complaints Commission has been informed.
Ch Insp Ian Marsh said: "We apologise unreservedly for what has happened.
"Police dogs and their handlers receive intensive training and play crucial roles in the arrest of suspects day in day out, but on the very rare occasions where things go wrong, it's vital we understand why and learn the lessons to ensure it doesn't happen again."
The incident happened at about 15:00 BST on Sunday after officers responded to a report of four men stealing wiring on Western Road, near Langley Green railway station.
A nearby resident described the attack as "disgusting".
She told BBC WM: "Are they going to put the police dog down? This is what we want to know.
"At the end of the day they'd do it to a normal dog so why not a police dog?
"My grandkids are always in this garden."