British officials say they have launched an investigation into how child welfare workers were unable to detect a man who raped his two daughters for years.

The unidentified 56-year-old Sheffield, England, man, known in court documents as Mr. X, was sentenced at Sheffield Crown Court Tuesday to 25 life sentences for imprisoning and raping his daughters over a 25-year period, fathering nine of his own grandchildren, The Times of London reported.

The family came into contact with social workers, doctors, teachers and police officers many times over that period but Mr. X's crimes were never detected. The Times said the Sheffield City Council has launched an inquiry, examining the roles of South Yorkshire Police, Lincolnshire County Council and Lincolnshire Police.

During testimony at the trial, Sheffield and Lincolnshire county officials both said that the family was known to them and several contacts with authorities that could have raised the alarm failed to do so, The Times said.

Mr. X's daughters said in a statement, "The suffering he has caused will continue for many years and we must now concentrate our thoughts on finding the strength to rebuild our lives."