Title: CAPTAIN AMERICA#320 by Mark Gruenwald (writer) and Paul Neary
Synopsis: Captain America learns of the massacre from the Water Wizard, who had planned to attend the meeting but arrived after the massacre was over due to a flat tire. Captain America sets a trap, pretending that Mirage was still alive, and feeding false info to the press [The press announced the truth soon after; a different Scourge heard the correct body count]. The original Scourge, after first making an unsuccessful hit on Diamondback and another Serpent Society member (can't remember whom; this might actually have occured in the previous issue; anyone know?), fooled into believing Mirage was still alive returns to the bar and gets captured by Cap, who was disguised as Mirage. Scourge turns out to be an anonymous white haired man who claims he was the Enforcer's brother. He says he killed the Enforcer to end the shame to the family, then continued the killing spree. Scourge is then shot to death by an assailant hiding in the bushes, who declares, "Justice is Served!"
Is it a key part of the overall Scourge storyline? Yes. Domino is introduced for the first time, giving Scourge info on various villains' whereabouts. The Scourge responsible for most of the original killings dies in this story. This is the first irrefutable proof that there is more than one Scourge.
Is is part of the main story in this issue? The whole issue is devoted to the hunt for Scourge
Comments: Scourge's assailant, according to Marvel Universe Masters is the same person who killed the Wraith
Oddly, the Enforcer's bogus story coincides with inaccurate info in the first Official Handbook of the Marvel Universe as to whom the Enforcer really was (both the original Ghost Rider stories and Marvel Universe Deluxe get the true alter ego correct; the latter even used the true scenario to point out why Scourge had to be lying, which was not clear from the issue of Cap itself)