Nikki’s mother, Sharon Henderson, 51, said: “It’s been a very emotional time.Credit:ncjMedia Ltd An arrest has been made in one of Britain’s longest unsolved child killings following a DNA breakthrough. Northumbria Police have detained a man in Stockton-on-Tees on suspicion of murdering Nikki Allan following a raid on a house in the town, 25 miles from where she died in Sunderland.Schoolgirl Nikki was just seven years old when she was found stabbed to death in a derelict building after vanishing from near her Sunderland home in October 1992. She had been stabbed 37 times.The force said the arrest, on Tuesday, was connected to a “historic offence”, and it confirmed on Friday that a man was held over the death of the seven-year-old. In a statement, a police spokesman said: “A man was arrested on suspicion of the murder of schoolgirl Nikki Allan. He has been released under investigation and enquiries are ongoing.”Nikki’s mother, Sharon Henderson, 51, said: “It’s been a very emotional time. When the police told me they had arrested someone it was such a shock I almost collapsed. Now he’s been released I don’t know what to think.” Last year, the 25th anniversary of Nikki’s murder, police revealed that they were examining new DNA evidence after a breakthrough in October. Nikki vanished on a Wednesday evening in October 1992 after leaving her grandparents’ in Sunderland’s Wear Garth. Neighbours formed search parties in a desperate bid to find the little girl but her body was later found in a derelict building a few hundred yards away, after her shoes were found outside.Breaking his silence about his daughter’s death last year, Nikki’s dad David Allan said: “I have remained quiet about Nikki’s death for 25 years but now is the time I need to speak out.“I can’t begin to describe how difficult life has been without my beautiful little girl. I would never want anyone to suffer the heartache we have suffered as parents.”In 1993, George Heron, then aged 24, stood trial for Nikki’s murder but was cleared by a jury at Leeds Crown Court.Then in 2014, Steven Grieveson, the serial killer known as “the Sunderland strangler”, was arrested and questioned on suspicion of Nikki’s murder. However, Grieveson was later told he would face no action.Crimestoppers had offered a reward of up to £10,000 for anyone with information that leads to the conviction of Nikki’s killer. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.