Fair enough..somewhat like Milarepa.Why not, a robber wrote the Itihasa, a carpenter became a poet, history is replete with such cases and moreover he already is suffering the consequences of his misdeeds. Until Kalki comes, it’s a painful existence for him. The man has suffered long enough…moreover if someone as pious as Prabhu Shri Ram, if his descendant can fight against the Pandavas at Kurushektra, anything can happen.
Exact reason behind it maybe someone more knowledge can highlight on that.
He killed many people through sorcery and witchcraft( following his mother's advice because his uncle had swindled all the family money)...but finally after feeling remorse he became a well know Siddha Purusha.