Police are closing in on those responsible for one of Northern Ireland's most notorious unsolved murders, a senior detective has said.
German backpacker Inga Maria Hauser (18) was last seen alive 30 years ago today on the Galloway Princess ferry from Scotland to Larne.
Her body was found buried two weeks later in Ballypatrick Forest in Co Antrim.
Detective Chief Superintendent Raymond Murray said the PSNI had a strong working theory of what happened, and the investigation was now focused on a small group of individuals.
He said detectives needed fractional pieces of evidence to bring them to justice.
"We've developed a belief over the past number of years that there's a small number of people in the community who are protecting those who are involved through some sort of misplaced loyalty," he said.
Mr Murray said it was possible the killer or killers were also aided by one or two others in the immediate aftermath.
"I think the 30th anniversary is an opportunity for those people to reflect. I know some people will think that's over-optimistic after 30 years, but I also know some people involved are struggling with this."
Mr Murray confirmed that all the suspects were still alive, though he declined to confirm whether they lived in the north Antrim area.
"They will know who they are," he added.
Specific appeals were made about the Munich teenager's movements on April 6, 1988.
One was for those who saw her on the ferry wearing a distinctive floral dress carrying a blue rucksack with a distinctive USAF (US Air Force) badge and two white shoes tied on.
Although police know she was on the boat, there has never been a confirmed sighting of her getting into a vehicle on the ferry or coming off the ferry across the land bridge. She had intended to make her way to the railway platform to journey south through Belfast to Dublin.
Mr Murray said any information on her movements would be "extremely significant" to the investigation.
DNA evidence recovered from the scene of her murder prompted a huge search by police to find a match, speaking face-to-face with around 1,700 people. However, no match was found.
"There may well be someone out there who already knows who that DNA belongs to," the detective said.
"We retain an open mind about it. We need to find that individual, and once we do, then the context of that DNA will become clear to the inquiry."
Further results from familial DNA testing, which covers the whole of the UK, are expected to be delivered in days.
Inga Maria's father Josef died from cancer and her mother Almut's poor health means she may never understand the truth.
Mr Murray recently visited her sister Frederica in Munich and said the loss still haunted her to this day.
"You could see the impact on her as soon as she walked into the room with German police," he said. "Within seconds of sitting down it all came back to her, it had never left her and she was very upset.
"She was very pleased we came over, but she described the impact it's had on her personal life over the years and how it has never left her, it is always in her mind. It's actually been one of the determining factors in her life in a negative way.
"Are we seriously going to let her go on another 15-20 years and not know who murdered her sister?
"I think there are people who know and are very close to the killer or killers."
A memorial service will be held in Ballypatrick Forest today, with an inscription stone unveiled by singer Keeley Moss and SDLP MLA John Dallat, who have campaigned for justice for Inga Maria.