Cicada

Cicada is a Metahuman mass murderer, targeting Metahumans specifically.

The Flash: Season 5
As he left a trail of bodies throughout Central City, Detective Joe West and his new partner Jack Sheriden were put on the case. Later after a plane crash, Cicada hunted down the one Metahuman in captivity of the CCPD, Gridlock and used his Lightning Dagger to nullify his powers and kill him, before disappearing without a trace.