user: Petra Pazsitka, then 24, was declared dead five years after she went missing from her student accommodation.
A man convicted of murdering a teenager who went missing nearby confessed to killing the young woman too.
However police investigating a robbery came across a tenant, a 55-year-old woman, who had no ID.
She told the officers that she had been living under a false identity and gave them her real name.
Ms Pazsitka's disappearance was the subject of an appeal on the German crime show "Aktenzeichen XY".
A spokesman for police in Braunschweig, the northern German city where Ms Pazsitka was studying computer sciences in 1984, said she had wished to remain undiscovered.
"She said only a little about the background of her disappearance and why she left back then," Joachim Grande said.
"She said that she had prepared for it and that she wanted it," he added.
Ms Pazsitka had withdrawn DM4,000 from her bank to start a new life, he said, and gave a student neighbour keys to her apartment to look after her pet birds.
He said the officially dead woman's elderly mother and brother were "absolutely shocked" when they heard she was still alive.
The family want to have contact, German media report, but Ms Pazsitka does not wish to see them.

Sum: German police say a woman who disappeared in 1984, sparking a murder hunt, has been found alive and well and living in Duesseldorf.


"I was the new kid at school and there just happened to be a goalkeeping position available," she tells BBC Sport. "Which always seems to be the case."
Unsurprisingly, there are not many children who volunteer to have solid hockey balls fired at them during bitterly cold mornings on the sports field.
But Maddie wasn't like most children.
Media playback is not supported on this device
"I used to throw myself around a lot in rounders. I would unnecessarily dive for a ball rather than step left or right, which I guessed showed an element of goalkeeping that the coaches picked up on," she recalls.
"So I was shoved in goal and it went from there."
Just over a decade later and 24-year-old Hinch is first-choice keeper for England and has earned 16 caps. She still has not quite got used to having balls shot at her, though.
"Any hockey goalkeeper who says they've never closed their eyes for a second and thought, 'please don't hit me' is lying. There are definitely those scary moments," says the Holcombe player, who wears protective goalie kit weighing up to 15kg during matches.
"It's something that you grow to enjoy, which sounds slightly weird. You're the last person in line and you can keep the team in it and potentially win games. It's a complete thrill."
Being able to watch us perform at an Olympic Games has inspired me even more to be a keeper at the next one
In June Hinch was awarded player of the tournament in her first real taste of international hockey as the country's number one - the World League Semi-Finals in London.
But it has been a tumultuous journey to the top. When England won a bronze medal at the last European Championships in 2011, she was the reserve keeper and did not play a game.
Then when Great Britain celebrated a bronze medal at their home Olympics in London last summer, Hinch was watching from the stands of the Riverbank Arena, having been left out of the squad.
"It was obviously incredibly hard, but with the goalkeeping situation we always knew Beth [Storry] was going to be number one," Hinch explains.
"There was always that option of being that second choice and being there in the village with the squad. To not get that was heartbreaking. But I think going and being able to watch us perform at an Olympic Games has inspired me even more to be a keeper at the next one."
Now that the next Olympic cycle is under way, the ultimate goal is winning silverware at Rio 2016. But first, Hinch and her relatively new group of team mates must negotiate the forthcoming European Championships in Belgium.
When England won bronze back in 2011, it was their fourth straight third-placed finish at a Euros and their seventh consecutive appearance in a bronze medal play-off. The previous year they also came third in the World Cup, Commonwealth Games and Champions Trophy events.
But this is a new squad - five players involved at London 2012 has since retired - with a new coach. Third place is not on their minds.
"In Chiswick [at the World League tournament], we did very well and surprised ourselves a little bit. So if we go in [to the Euros] with that open mind and not put too much pressure on ourselves, I can't see why we can't make the final," says Hinch.
England head into the competition as the second-highest ranked team. But new coach Jason Lee has altered the squad's playing style to more "open, fast, exciting hockey", as Hinch puts it.
"Jason is trying to bring in some new ideas. He's convinced us that it will work," says Hinch. "We can definitely see in some of the training games that it doesn't quite work. We might have the odd result where everyone might go, 'Ooooh', but we're looking long term."
Find out how you can get involved in hockey by going to our  pages or England Hockey's Back To Hockey page.

Sum: Maddie Hinch smirks when she remembers how she drew the short straw to become a hockey goalkeeper.


About 250 demonstrators blockaded the Muller Wiseman plant in Market Drayton, Shropshire, from 21:00 BST on Monday.
Protest group Farmers for Action said its members voted for the action in response to falling milk prices.
Muller UK & Ireland Group chief executive Ronald Kers branded the group "militants" and said blockades could damage the dairy industry.
He said a worldwide surplus of milk coupled with weaker demand had driven down the price of dairy products.
Muller was one of a number of major milk processors which recently announced it would lower the price it paid for milk.
David Hanley, chairman of Farmers for Action who was at the protest, said the future for dairy farmers was uncertain.
"It's very simple," he said.
"For the last three or four months, we have been telling this processer and all the other processers that the milk price cuts they're making aren't sustainable and they are going to put a lot of dairy farmers out of business."
He said the the current problem of over production in the UK was only "1% between supply and demand and that is not extreme".
"These people are using every excuse under the sun to take advantage and cut milk prices. Why? Because they can. Why? Because we are the weakest link."
Sam Jones, a member of Newport and Wem Young Farmers, also at the protest, told BBC News it was important to get the message out to the public that their future was in jeopardy.
"It can't be right," he said.
"We're doing a 100-hour week for less than the cost of production.
"We're just not going to be able to keep going."
But Rob Harrison, chairman of the National Farmers Union national dairy board said: "It is really tough that actually we're in a global marketplace, that is the way it is.
"We trade in dairy products.
"We can bring imports in, exports out, etc etc and actually that is the price."
Farmers For Action said it planned to stage a second protest on Wednesday in Bridgwater, Somerset and would also target supermarkets in the coming weeks.
The National Farmers Union (NFU) has urged supermarkets to pay more for milk.

Sum:

assistant: Hundreds of farmers have staged a protest over milk prices outside one of the UK's largest dairies.