New DNA evidence could finally solve the murder of a seven-year-old girl who was found dead 25 years ago, police have said.

Nikki Allan's body was found badly beaten and stabbed 37 times in a derelict building near to her family home in Wear Garth, Sunderland, on 8 October 1992.

Her murder shocked the country. Despite lengthy police investigations and a murder trial, nobody has been convicted over the death.

Now 25 years later, Northumbria Police say advances in technology have allowed them to recover further forensic evidence – including DNA from an unknown male – which could help the investigation.

They have appealed for male members of Nikki's family, friends or others who may have innocently come into contact with her to provide a DNA sample so they can be eliminated from enquiries.

The first person to step forward was Nikki's father, David Allan, who broke a 25-year silence to show his support for the police investigation.

"I have remained quiet about Nikki's death for 25 years but now is the time I need to speak out," he said on Friday (6 October).

"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.

"As Nikki's father, I have provided a DNA sample myself and it is very quick, easy and completely painless. I would beg anyone who knew Nikki or had any contact with her before she died to please come forward to have your DNA taken.

"This isn't about accusing anyone of being a suspect – this is to eliminate you from police enquiries."

Nikki's mother, Sharon, added: "Please, please come forward. Anyone who has any information, no matter how small you think it may be just come forward to police.

"I have met the team investigating Nikki's murder and have confidence that we will eventually get the justice we have waited for for 25 years."

The charity Crimestoppers has also offered a reward of up to £10,000 for anyone who has information which leads to the apprehension and conviction of Nikki's killer.

Only one person has faced trial over the girl's death – her then 24-year-old neighbour, George Heron. The case against him collapsed, however, after a judge said officers had used "oppressive methods" to obtain a taped confession from him.

Detective Inspector Paul Waugh said: "Nikki would have been 32 years old this year and it is utterly heartbreaking to hear from her parents and close family talking about what could have been for Nikki – she may well have had children of her own by now and this is something that haunts both David and Sharon greatly.

"If anyone has any information at all please contact police. It may be something they believed at the time was not important but this could be the vital clue we are looking for. Or anyone who may have been in the area at the time of Nikki's death and wish to provide a DNA sample then please come forward. If you know anything, no matter how insignificant you may think it is, then call us or contact the charity Crimestoppers anonymously."

Anyone who wishes to speak to police or pass any information on is asked to contact the major crime team on 101 ext 69191 or the independent charity Crimestoppers on 0800 555 111. Only those passing information through Crimestoppers will be illegible for a reward. Information passed to the police will not qualify.