In The Dante Club, who was murdered fourth and how?

In The Dante Club by author Matthew Pearl, there are only three murders. The attempted fourth murder is prevented when the members of the club walk in and save the victim, Dr. Manning, before the murderer can kill him. Dan Teal, a veteran who has gone mad and merged his identity with Dante's, taking it upon himself to avenge all of the writer's critics and opponents, is subsequently killed by Manning. However, this act would be considered self-defense rather than murder.
Longfellow was the first to realize that the killer was racing the club to complete the translation of the Inferno. Dr. Manning would have become the killer's fourth victim since he works as the Harvard University treasurer. This position put him on the killer's list since the university was highly critical of Dante. In an attempt to recreate one of the punishments for the damned souls in the Inferno, a theme which all the other murders follow, Teal attempts to kill Dr. Manning and Pliny Mead by burying them in ice without clothing. After fleeing the scene of the attempted fourth and fifth murders, Teal turns on The Dante Club and tries to punish them as well. Manning finds Teal holding a gun to Longfellow and kills him, bringing the story to its resolution.