How it is possible to make a candala a Vaisnava?" No, that is possible. Prabhavisnave namah. Visnu is so powerful, omnipotent. He can do that. So only by Visnu mantra, by becoming a Vaisnava, one can transcend all this restriction, sociology
-Lecture on Bhagavad-Gita 1.40 -- London, July 28, 1973

प्रायेणैतद् भगवत ईश्वरस्य विचेष्टितम् ।
मिथो निघ्नन्ति भूतानि भावयन्ति च यन्मिथ: ॥ २४ ॥
Factually this is all due to the supreme will of the Lord, the Personality of Godhead. Sometimes people kill one another, and at other times they protect one another.
-Shrimad Bhagvatam Canto 1 Chapter 15 Verse 24