Viewers of Daredevil: Born Again might be confused over how Dumb Benny relates to what happens to Foggy. In the episode before the finale, Daredevil has an epiphany on a case that Foggy had been working on, which turns the entire motive behind Poindexter’s actions on its head. It’s also been many episodes since we’ve heard about Benny, so it’s good to catch up on the details of the case, since the Daredevil Season 4 finale will likely provide some clarity on the entire incident. (Warning: Spoilers ahead!)

What does Daredevil’s Dumb Benny have to do with Foggy’s death?
Benny, who Foggy nicknames “Dumb Benny,” is a client of his that stole merchandise from the Red Hook pier, which is controlled by Vanessa and Wilson Fisk. This is what ultimately results in Foggy’s death, as whatever he learned from the case was apparently important enough to Fisk’s dealings that he was targeted for an assassination by Poindexter.
As explained by Kirsten McDuffie in the first episode of Daredevil: Born Again, Benny had stolen twenty cases of Lafite Rothschild, which is a very expensive wine, from a bonded warehouse in Red Hook. Unluckily for him, the seedy operations of Fisk’s underground empire with the Five Families run out of this pier, which Wilson Fisk later hopes to revitalize with his mayoral port project, so it’s possible that this wine happened to be a part of their inventory or Benny learned something incriminating about Fisk.
Either way, whatever Benny found out was serious enough that Foggy attempted to protect him as his client and stashed him away at his apartment. The case with Benny was going well enough in court that Foggy believed that he was going to win, which is why he was celebrating by drinking a shot of O’Melveny’s at the bar. However, Poindexter is quickly hired to find Benny, rough him up enough to get Foggy’s location, and assassinate him. It was originally presumed that Poindexter, or perhaps Wilson Fisk through him by proxy, was merely getting revenge on Daredevil, but he realizes that Vanessa was the culprit.
It’s still unclear what Benny and Foggy learned that was so dangerous to get them killed, but we’ll likely find out in the finale. If Matt Murdock can uncover the reason, he can potentially take down the Fisks and get justice for Foggy.
That said, some fans are still convinced that Foggy is actually alive after all this time.