History
According to his father Ralph Losani, his son Fabian was kidnapped by Teodor Zarco the leader of the Black Knife Cartel. Upon discovering this Ralph hired Bullseye to return his son safely back. After Bullseye confronted the Black Knife Cartel and was able to catch up to Fabian freeing him of his current captors, Fabian shot Bullseye.
After which it was revealed that Fabian wasn’t kidnapped at all, but was partnering with the Black Knife Cartel for financial gain in hopes that with their help he could become bigger than the Kingpin.