The Tanzanians searching for their grandfathers' skulls in Germany

Isaria Anael Meli has been looking for his grandfather's remains for more than six decades.

He believes the skull ended up in a Berlin museum after his grandfather, Mangi Meli, along with 18 other chiefs and advisers, was hanged by a German colonial force 123 years ago.

After all this time, a German minister has told the BBC the country is prepared to apologise for the executions in what is now northern Tanzania.

Other descendants have also been searching for the remains and recently, in an unprecedented use of DNA research, two of the skulls of those killed have been identified among a museum collection of thousands.

It is rare to find an acacia tree on the lower slopes of Mount Kilimanjaro. Its twisting branches reach above the steep road and stand out among the denser lush vegetation.

At one time, it shaded a market for the villagers of Tsudunyi, a part of what is now called Old Moshi, who lived off the fertile land and enjoyed the cooler temperatures that the higher altitude brought.

But this focal point for the community became the scene of a great tragedy. Despite the peace of the natural surroundings today, its impact has reverberated down the decades.

It was here on 2 March 1900 that, as the descendants tell it, one-by-one the 19 men were hanged. They had been hastily tried the day before, accused of plotting to attack the German colonial forces.

Germany's claim to this part of the continent was formalised at the Berlin Conference of 1884-1885. The European powers divided up Africa between them, without the people living there having any say in what happened.

Mangi Meli, the most prominent mangi, or chief, among those who were killed, had in 1892 successfully defeated the German forces. That success was later reversed and by the end of the 19th Century, the Europeans were keen to stamp their authority on this part of what was known as German East Africa.

They wanted to make an example of Mangi Meli and other local leaders who may have been planning an uprising.

This 1910 postcard is believed to show the acacia tree where the men were hanged in 1900

The humiliation did not end there.

While most of the torsos are believed to be buried in a mass grave somewhere near the tree, their heads were at some point removed, packed up and sent 6,600km (4,100 miles) to the German capital. In some cases the complete skeletons were shipped.

When speaking about what happened to his grandfather, Mr Meli does not sound angry, but there is a sadness in his voice and a sense of bewilderment that this was allowed to happen.

The lively 92-year-old was told about the killing of Mangi Meli by his grandmother, who he says was forced to watch the execution, and explains that the chief came to him at night telling him that he would return one day.

"Always, always, always he was coming to me in my dreams," he says.

His floppy sun hat and twinkling eyes when he smiles disguise his tenacious personality.

Since at least the 1960s, Mr Meli had been writing to the German and Tanzanian authorities urging them to look for the remains of his grandfather.

He says officials tried to put him off by telling him that relevant records had been destroyed during World War Two. But Mr Meli was not deterred.

"Visitors are always crying: 'Tell all the people of Germany to return the skull.'

"They kept it somewhere just because they thought the Mangi Meli family were small people - believing that they could do what they wanted. But remember that this skull is needed by the whole country - not me, myself, only."

There is a sense of profound loss that goes beyond the idea that this was a historical injustice.

Mangi Meli was a chief from the Chagga ethnic group - one of the most prominent in modern-day Tanzania. For the Chagga people, as well as others in the region, the idea that the head was separated from the body and then taken away from the land is deeply disturbing.

Mangi Meli's early success in resisting the Germans was later reversed

In Chagga culture the dead are supposed to be buried in the homestead so they can continue to watch over the living. It is believed that the failure to do that could have consequences down the generations.

"If we leave the skulls in Germany, the spirits will be tormenting these families," explains Gabriel Mzei Orio, who founded the Old Moshi Cultural Tourism Enterprise in part to highlight Chagga culture to the rest of the world.

He is standing under the acacia tree in Tsudunyi, next to a memorial to those who were killed there.

"The spirits are saying: 'You know where we are and you don't bring us to our homeland and you know we were taken in a cruel way.'"

Simulango Molelia, the grandson of another victim of the executions - Mangi Molelia - believes his family is being haunted by the chief's spirit.

The 69-year-old sits in his shady homestead surrounded by banana plants, the staple food in the region and the source of the traditional beer that the family brews. As is the custom here, the graves of his mother and father are in the homestead - a tradition denied to his grandfather.

Simulango Molelia believes that his family has suffered as a result of what happened to his grandfather's remains

"Many things were affected by the killings," he says in a soft voice, suggesting that it was like roots of a tree being attacked.

"When Mangi Molelia was killed, the family lost its wealth. Up to now things are not good."

But for those who took the body parts more than 120 years ago, this was of no concern.

Museums and other institutions in 19th and early 20th Century Europe and North America amassed large collections of skulls and other human remains.

This was partly driven by huge interest in the now-discredited science of phrenology. It was based on the idea that someone's fundamental characteristics were reflected in the shape of their skull.

In some cases it took on a racist element, with researchers trying to establish a racial hierarchy. As a consequence people began collecting skulls from across the world.

German anthropologist Felix von Luschan, who headed the Africa and Oceania department of Berlin's Royal Museum of Ethnology, was keen to acquire remains from Germany's empire as well as other European colonies.

"Even an amateur can procure anthropological material," he wrote in 1899 in an instruction manual for collectors.

"Any occasion to rescue a large number of skulls preferably with lower jaw should be zealously used…

"In certain circumstances a very superficial cleaning is necessary. Sometimes this entails only the removal of flesh and drying - the rest can be done in Europe."

In March 1901 - a year after the executions - Von Luschan wrote directly to First Lt Moritz Merker, one of those in charge of the German forces in Kilimanjaro.

The letter was about some cultural artefacts, but as a final paragraph he wrote: "I use this occasion to inquire whether it would be possible for you to ask natives in an amicable way to hand over some skeletons of Maasai and Chagga to us."

Merker responded the following month, saying that some remains were on their way and a shipping note from the port of Dar es Salaam states that two boxes of Chagga and Maasai skulls had been sent.

It is not clear if Mangi Meli's skull was among the shipment, but it seems likely that this was when some of the remains of the executed men were transported, according to German researcher Konradin Kunze, who has been heavily involved in the campaign to find them.

The bones then went into Von Luschan's vast archive, including the S-collection ("s" for skull), which in the four decades up to his death in 1924, grew to 6,300 samples.

Some of his private collection was sold by his widow to the American Museum of Natural History in New York. This included the entire skeleton of one of those hanged in 1900.

But for the rest, down the decades, they passed through several institutions and in 2010 they ended up in the care of the Berlin-based Prussian Cultural Heritage Foundation (known by its German initials SPK) - but much of the documentation that went with it had been lost.

Zablon Ndesamburo Kiwelu followed in his late brother's footsteps and took up the search for the skulls

"What the Germans did was not a good thing," says Zablon Ndesamburo Kiwelu, whose grandfather, Mchili Sindato Kiutesha Kiwelu, served as an adviser, or akida, to Mangi Meli and was also hanged.

The 75-year-old former accountant, dressed in a smart black blazer, is very matter-of-fact in his assessment.

"We are waiting for the skulls to be returned to this country so that we can be happy, because we are not happy."

But in order for any return to happen, the skulls needed to be identified. This was a seemingly impossible task, given the vastness of the Von Luschan collection and the lack of documentation.

The SPK, which had the large collection of human remains, said it was committed to finding out where they came from.

While researchers may have been able to figure out their approximate origins, to identify who the skull once belonged to was thought to be near impossible.

Some of the descendants of those hanged thought that a DNA comparison might help, and they approached Mr Kunze from the arts company Flinn Works, which had mounted an exhibition about the remains, to see if this could be organised.

He then helped get the swabs in Tanzania and, with pressure group Berlin Postkolonial, persuaded the SPK to conduct an analysis on some of the remains.

Mr Kiwelu (L) and Mr Meli (R) have campaigned together to get the remains returned

SPK researchers were helped by the fact that some of the skulls had catalogue markings etched on to them, including the word "Wachagga", which meant that a guess could be made about where they came from.

They identified eight skulls in the collection that could have been related to the 1900 hangings.

The descendants' DNA samples were taken to Germany and then the painstaking work to find a match got under way.

Dr Janine Mazanec is a biological anthropologist at the University of Göttingen and often works with archaeologists on historical burial sites. She has also worked with the police to help identify victims of a crime.

This, though, was an unusual project.

One of the things she noticed about some of the skulls that had been sent to her laboratory from Berlin was that they had cut marks "indicating that these were not taken from a cemetery" after the body had decomposed but rather that the flesh had been removed from the head soon after death. This was another clue that they could have something to do with the executions.

In order to discover the DNA, Dr Mazanec had to take a molar from the jaw, remove the root and carefully return the tooth.

The root was ground down and then through a chemical process the DNA was extracted, which contained the crucial information.

This was then compared with the samples that the grandsons had provided. What Dr Mazanec was looking for was a match with the DNA from the Y-chromosome, which is passed through the male line, from son to son.

She discovered a complete match for one of the skulls and then an extremely likely match for a second skull.

The skull of Mr Kiwelu's grandfather had been found - and likewise for Mr Molelia. But Mangi Meli's remains were not identified.

Dr Mazanec says that to her knowledge this was the first time that this kind of DNA analysis had been used to link known individuals in the present with the remains of named individuals that have ended up in a skull collection.

For some, the decades-long search had not been in vain and the families had been vindicated.

Mr Kiwelu proudly shows the letter from the SPK confirming the results of the DNA comparison.

"This news is a small miracle for us and makes us very happy. I hope that [it] will also bring you joy," SPK president Dr Hermann Parzinger wrote. He added that work could now begin on the repatriation of the remains.

Mr Kiwelu says he read the letter out to his family.

"We were very happy that the skull would be returned."

Mr Molelia wants the skull of his ancestor to be brought to Tanzania and "buried in our Chagga tradition".

Talks between the German and Tanzanian authorities are taking place in order to facilitate moving the skulls, which can be a complex process.

A bust honouring Mangi Meli now sits under the tree where he was hanged

But attention now turns to the German government and the reckoning with its colonial past.

"Germany is facing up to its historical responsibilities… [and] is committed to advancing the process of coming to terms with the injustices committed," Katja Keul, a minister of state in the foreign ministry, wrote in an email response to a list of questions.

The hanging of the 19 men 123 years ago is one of the "numerous crimes" that she referred to.

Asked directly if Germany was prepared to issue an apology for the executions, she said "yes", but did not go into any details about what form this would take.

But Mr Meli - the grandson of Mangi Meli, whose skull has not been found - is left frustrated after the decades of searching.

He is convinced that it is still in a museum collection somewhere.

"I am suffering because I have spent money to fight this and to get what?"

But he is not giving up.

"I want to see my grandfather before I die."