Police gave relatives what they believed were the remains of a dog found in the rubble of a Sunday house fire in Ibaraki Prefecture, only to later admit the remains may have been part of the corpse of an occupant of the home who apparently perished in the blaze.

The early Sunday fire, which is believed to have originated in the Mito home of Yoshio Katogi, 54, and his wife, Sachie, 54, ultimately burned down four houses, accounting for 810 sq. meters. The couple remain unaccounted for but police said Wednesday they believe the pair were killed in the blaze.

Soon after the fire, Mito police told the couple's next of kin that two bodies had been found in the rubble, but later said one of them was that of a dog.

Investigators discovered the first body before noon Sunday and hours later found other charred body parts, which they judged on the spot were the remains of the couple's pet dog.

They handed over the body parts to the couple's relatives without bothering to perform an autopsy. The family later contacted the police asking them to double-check the identity of the remains.

An autopsy proved the police had erred.

"We'd like to offer a sincere apology to the family," said Yoshiharu Miyauchi, head of Mito police, adding that it will take preventative measures to prevent a recurrence.