Narada informed Kamsa that in his previous birth Kamsa was Kalanemi, a demon killed by Visnu
SB Canto 10.1 to 10.13
Other Books by Srila Prabhupada
Krsna, The Supreme Personality of Godhead
This action of Kaṁsa is not very difficult to understand. There are many instances in the history of the world of persons in the royal order who have killed their father, brother or a whole family and friends for the satisfaction of their ambitions. There is nothing astonishing about this, for members of the demoniac, greedy royal order can kill anyone for their nefarious ambitions.
Kaṁsa was made aware of his previous birth by the grace of Nārada. He learned that in his previous birth he had been a demon of the name Kālanemi and that he had been killed by Viṣṇu. Having now taken his birth in the Bhoja family, he decided to become the deadly enemy of the Yadu dynasty; Kṛṣṇa was going to take birth in that family, and Kaṁsa was very much afraid that he would be killed by Kṛṣṇa, just as he had been killed in his last birth.He first of all imprisoned his father, Ugrasena, because he was the chief king among the Yadu, Bhoja and Andhaka dynasties, and he also occupied the kingdom of Śūrasena, Vasudeva’s father. He declared himself the king of all such places.