'The truth is out there': Million-dollar reward for information over murdered German backpacker

Six days later, Ms Strobel's body was badly decomposed, naked, and covered with palm fronds at the sports ground about 90 metres from the campsite. Dental records were used to confirm her identity.

At the time, Mr Suckfuell described his girlfriend's death as an "assassination" and called for "this bloody evil monster" to be brought to justice.

"Simone was full of love and happiness," he said. "The last couple of months, when she travelled through Australia, she said it was like living in paradise.

"She was an angel on earth and we can't understand why Jesus took her away. Nobody can answer this question but everybody can see her bright shining star now."

On Thursday, a $1 million reward was announced — available to anyone in the world — for information leading to the arrest and conviction of those responsible for Ms Strobel's death. Police Minister David Elliott said the reward was a substantial incentive for anyone with information.

"For 15 years, police have been determined to uncover the truth of what happened to Simone, both the Lismore community and her loved ones in Germany deserve answers," Mr Elliott said.

Richmond police District Commander Superintendent Scott Tanner said police believe there are people in Australia and overseas in Germany who are withholding vital information.

"We know the truth is out there, and we know there are people who are holding it back," he said.

"Strike force detectives have worked for more than a decade, trying to piece together Simone's last movements and who was there in her final moments.

"We have continued to examine evidence and speak with witnesses over the past 15 years, but we need additional help from the public to finally determine what happened to Simone."

"This is a crime which has stuck with many families who have young relatives travelling the world; the thought of losing them so far away from home is hard to comprehend. Help us to put Simone's family at ease," he urged.

"Police are very confident we will solve this matter," he said.

Superintendent Tanner added that Mr Suckfuell "remains a person of interest in this investigation", but investigators were keeping an open mind about the circumstances surrounding Ms Strobel's death.

He said Ms Strobel's family was hopeful that the reward announcement would encourage people to come forward.

In 2007, a coroner found no definite cause of death could be established, but it was most likely Ms Strobel died of suffocation or smothering asphyxia.

The inquest heard that the group had gone to a pub, where Ms Strobel was reduced to tears after arguing with Mr Suckfuell. Another row followed at the campsite, witnesses said, after which Ms Strobel stormed off.

Deputy NSW coroner Paul MacMahon said there was insufficient evidence to recommend charges.

In 2014, German police offered a 10,000 euro reward for information leading to the resolution of the case. The reward remains on offer.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000