A former German nurse has emerged as the country's worst ever serial killer after police linked to at least 106 deaths.

Niels Högel, who is already serving a life sentence for six murders, is suspected of killing the patients during his time working at two clinics in northern Germany.

But astonishingly he is only known as Niels H. inside the country because reporting restrictions mean journalists are legally blocked from releasing his second name.

Niels Högel, a former nurse, has emerged as Germany's deadliest serial killer after being linked to the deaths of at least 106 patients he administered with lethal drugs

German privacy laws mean authorities will not fully identify criminals, sometimes even after they have been convicted.

Suspects in criminal cases are often only identified in German media by their first name followed by the first letter of their surname.

Journalists only printed the first name of Berlin truck attack Anis Amri and censored his face, even while asking the public to help track him down.

Högel was jailed back in 2015 after admitting to police that he injected two patients with life-threatening drugs before trying to revive them in order to play the hero.

When quizzed further by police he said he was unable to remember the full extent of his activities, though bragged: 'To be honest I stopped counting after 50.'

That lead authorities to exhume 134 bodies at cemeteries in German and as far afield as Turkey and Poland in their search for the truth.

Investigators have now linked Högel to 106 deaths but say the total is likely far higher because many patients who died in his care were cremated, obliterating any evidence that would have implicated him.

He will now face charges of killing a further 100 people at two clinics next year.

Högel is believed to have administered the drugs so he could revive the patients and play the hero, before eventually killing them

Inquiries into how he was allowed to go on killing for so long will likely continuing long after he died behind bars, but it is clear that bureaucratic inertia coupled with fears of police probes costing executives their jobs were partly to blame.

Högel was born on 30 December 1976 in the German port city of Wilhelmshaven.

He grew up in a Catholic household he would later describe to his court appointed psychiatric expert Konstantin Karyofilis as 'warm-hearted and sustainable.'

Högel's father is a nurse out of conviction and a solid supporter of the SPD - Germany's Labour Party equivalent.

His mother trained as a lawyer's assistant but only found work as a cleaning lady.

Högel has an older sister who later became a dental assistant.

'A thoroughly helpful family', say acquaintances from Wilhelmshaven. 'Helpful, kind, caring,' said a neighbour to a local radio station.

The first sign of trauma in the family came when Niels was 11 as his parents briefly split, which appeared to have a profound effect on his young mind.

During this period, he told his psychiatrist, he developed 'fears, insecurities.'

His performance at the local comprehensive school, hitherto all A's, slipped.

He assumed the mantle of 'class clown' - a role guaranteed to bring him some of the attention he craved.

Högel decided at 16 that he wanted to become a firefighter but discovered he suffered from vertigo, and entertained thoughts of being a doctor but found the study too difficult.

He dropped out of school shortly before his Abitur exams, the German equivalent of A Levels, before deciding to become a nurse like his father.

At the age of 17 he began nurse training at the St. Willehad Hospital where alcohol and drugs began to occupy a large place in his life, he later told police.

He passed the nursing exams with 'mediocre' results and 1999 he started at the highly-regarded heart surgery intensive care unit of the Oldenburg Clinic.

Högel struggled early on with the demands of the work, describing the first surgery he assisted on as a 'traumatising experience'.

He is already serving life in jail for six murders, but is due back in court next year to face charges over 100 more deaths. Police say the full extent of his crimes will never be known

He went on to develop depression and anxiety and began to drink more as a result.

An attention-seeker from birth, Högel uses his access to potentially lethal drugs in an attempt to play the hero.

His first known murder was carried out in February 2000 at the clinic in Oldenburg in Lower Saxony, close to the Dutch border, where he injected a patient and attempted to revive them without success.

After killing at least another 35 patients, he moved in 2002 to a hospital in Delmenhorst near the north-western city of Bremen, where he resumed his grisly practice within a week of starting his new job.

It is believed Högel was suffering from a rare condition known as Munchausen by Proxy syndrome, in which sufferers harm in order to act as 'reviving angel'.

Högel's preferred drug of choice were potassium-based medication used to treat heart patients with circulatory problems, though he would use five different types of cardiovascular medications over the next few years.

But his grim practices soon began to attract attention, with a coworker noting down all of the deaths and resuscitations that take place while he is on duty.

In just one weekend the worker noted there were 14 re-animations to five patients.

All of the patients ultimately died, but rather than calling the police, Högel's bosses simply transferred to another department, anesthesia.

Fearing that the net may be closing in on him at Oldenburg Hospital he applied for another job in nearby Delmenhorst in 2002 and began work there on December 15.

A week later, he killed his first patient there.

In 2003 and 2004, superiors note, the death rate on the intensive care unit was about twice as high as in previous years.

The consumption of the drug Gilurytmal - his preferred killing tool - was seven times higher than usual, doctors noted.

But still nobody reported the young nurse to authorities or raised concerns.

Even after Högel was caught injecting a 63-year-old patient who died shortly after, superiors took no action.

It was only towards the end of that year a leading doctor at the hospital carried out an audit on the cardiac drugs, calculated the number of patients who had died while Högel was on duty, and went to the police with his suspicions.

Högel was arrested and sentenced to seven and-a-half years imprisonment for murder in 2008, a sentence upped to life in 2015 after he confessed to more deaths.

His parents are still alive in Wilhelmshaven and have been to see him inside.

'The victims were play figures for him in a game in which only he could win and the others could lose everything,' said the presiding judge in his 2015 sentencing.

Ten years ago, a German nurse was convicted of killing 28 elderly patients, saying he gave them lethal injections because he felt sorry for them.

He was sentenced to life in prison.