Police say 'we're getting closer'
The sister of Inga Maria Hauser has made a heartfelt plea to anyone with information about her murder to come forward.
Last month police renewed their appeal for information and launched a new operation spanning Northern Ireland and Scotland in the hunt for the 18-year-old's killers.
Inga Maria was found brutally murder in a forest outside Ballycastle in 1988 - 14 days after she was last seen alive on a ferry from Scotland. No one has ever been convicted of the attack.
In the intervening years police have tried to trace the culprits and at one stage staged a large-scale DNA screening of people.
They said over 30 calls have been made to police since their anniversary appeal and they believe they are getting closer to catching those responsible.
Friederike Leibl has written an open letter to the people of Northern Ireland in a bid to encourage anyone with information about her sister's killing to contact the PSNI.
She wrote: "It's been nearly 30 years since my younger sister Inga-Maria was so brutally murdered, you cannot imagine how the murder of my sister has affected my family - we are broken inside.
"My father was worst hit - he fell ill with prostate cancer in 2005 and was treated for depression when the whole body was full of cancer.
"The fact of being confronted with this murder for a lifetime is just cruel, sick, sick. So I ask you to come forward with information, otherwise my sister's soul will never rest."
Inga Maria's body was found dumped in a remote part of Ballypatrick Forest outside Ballycastle, Co Antrim. Detectives believe a number of people may have been involved either directly or in the cover-up, and have previously said they only need fractional pieces of evidence to bring the chief suspect or suspects to justice.
A man in the rural area east of Ballymoney in Co Antrim was seen soon after the murder with scratches on his face, sparking rumours in the community that he had been involved.
Police said Inga Maria was subjected to a "vicious and ruthless assault".
"We believe members of the public may hold vital information about who killed the teenager and as a result received over 30 calls which we are currently assessing," said Detective Chief Superintendent Raymond Murray.
“Some of the developments over this period have been interesting and are being progressed by the investigation team.
“One strand of the operation was to identify the man whose DNA was found at the crime scene. A previous DNA screening process was one of the largest ever conducted and involved many hundreds of people, throughout the UK.
"However, as time evolves so does DNA science so we have carried out further familial DNA screening. We have now received the results and have met with scientists and other specialists in order to take these forward.
“We still believe we are extremely close to progressing criminal justice action against Inga Maria’s killer or killers.”
Detective Chief Superintendent Murray said anyone with information about who killed Inga Maria owes it her family to come forward so they can have closure after 30 years.
“After 30 years, it's time to tell us what you know - contact Police by calling detectives in Maydown on 02871379783,” he added.