[7] From 1999 onwards, Högel was employed at the Oldenburg Clinic, stationed in its cardiac surgery intensive care unit, Ward 211.
[8] In August 2001, doctors and medical orderlies at the hospital held a meeting, which Högel attended, discussing an unusual spike in both resuscitations and deaths during the preceding months.
In September 2002, the Oldenburg Clinic's head physician confronted Högel after multiple patients under his care had been found in life-threatening conditions for seemingly inexplicable reasons.
Therein, she testified to Högel's "circumspect, diligent and autonomous" work ethic, as well as to him having acted "prudently and in an objectively correct manner in critical situations".
In later court proceedings, it was reported that Högel had initially been held in high regard in Delmenhorst until suspicions against him began to arise.
His superiors allegedly did not act on these suspicions, even when four empty vials of gilurytmal (ajmaline) surfaced in Högel's ward, in spite of no doctor having prescribed any such medication at the time.
[12] On 22 June 2005, colleagues caught Högel intentionally manipulating a patient's syringe pump to improperly administer ajmaline.
To "sustain this euphoria, this feeling of happiness" he admitted later to have injected a severely ill intensive care patient with a toxic agent during his first night on duty after her birth.
Multiple coworkers of Högel's at Delmenhorst came forward to voice their suspicions that he was behind numerous complications, resuscitations and unexplained deaths at their hospital.
In December 2006, adjudicating the 22 June 2005 incident, the Landgericht Oldenburg (German regional court) sentenced Högel to five years in prison and an employment ban of equal length for attempted voluntary manslaughter.
From November 2014 onward, the special commission "Kardio" examined further deaths during Högel's tenure as a nurse at various places of employment.
[25] According to an August 2017 statement by the director of the special commission "Kardio", the "provable Oldenburg and Delmenhorst homicides [...] were only the tip of the iceberg".
Högel admitted to an undisclosed number of deaths but in most cases was unable to remember specific details, although he did not deny possibly being responsible.
[27] In November 2017, the total number of victims attributed to Högel was revised and increased to 106, with some suspicious deaths still under investigation.
[29] The police reported that Högel had made use of multiple drugs, including ajmaline, sotalol, lidocaine, amiodarone and calcium chloride.
Excessive doses of these drugs can cause cardiac arrhythmia and severe drops in blood pressure, which can lead to rapid physiological deterioration in patients already unwell.
[31] On 7 March 2018, the Oldenburg labour court sentenced Högel to pay 47,000 Euro in compensation, for two medical opinions and various lawyers' fees.
[31] Out of the 100 murder charges, Högel confessed to 43 on the first day of trial,[35] stated he could not recall 52 and denied his involvement in the five remaining deaths.
[37][1][31] The court described Högel's motive, to emerge as a hero after a potential reanimation, as "base" ("niedriger Beweggrund"),[38] which is a precondition for a murder conviction in Germany.
[31] Only then would he be obligated to testify at the trial against those employees, because until he had received a final verdict he still had the right to refuse testimony, and he had stated that he wished to exert that right.
According to the prosecution, the accused suspected Högel's involvement in the patient's deaths but neglected to take action, in order to protect the reputation of their hospitals.