German nurse Niels Hoegel used his job and access to medications to kill more than 100 people. He was convicted of two counts of murder and two counts of attempted murder in 2015, but recent studies have found that number to be much higher. Hoegel worked at an Oldenburg clinic from 1999 to 2002 and in Delmenhorst from 2003 to 2005.
During his trial he admitted to intentionally administering drugs to bring about cardiac distress in more than 90 patients in Delmenhorst because he enjoyed being able to resuscitate them.
Since his conviction prosecutors have exhumed 134 bodies from 67 cemeteries to run tests and toxicology reports. Multiple reports were inconclusive.
Police said that if hospital staff would have reported sooner, many lives could have been saved. Criminal cases are already being pursued against former staff at the medical facilities.
http://www.bbc.com/news/world-europe-41930177
http://time.com/5112257/niels-hoegel-germany-nurse-patients-murder/