Health,
That is from Rav Klein’s psak, and Rav Klein just said he cannot confirm the third-hand hearsay to that effect. So even R. Klein’s psak is saying no source for such claim! Secondly, even that hearsay from the Professor’s book is not claiming anyone said he was a rodef.
If you read Rav Elyashev’s psak (quoted earlier in the thread), R. Elyashev said “tikun olam” not rodef. AND R. Elyashev said the proof must be “CERTAIN” before one is allowed to call the police or authorities.