Nurse killed 300 patients. Why wasn't he stopped?

Niels Hogel, 42, is considered the most prolific serial killer in the history of peacetime Germany, and perhaps in the world. Officials suspect that as many as 300 patients may have died by his hand over 5 years starting in 2000. The number of killings and amount of time it took for suspicions to come to light have raised uncomfortable questions for Germany.

from Times of India http://bit.ly/2HeGNaL