The Red Death described in The Man of Bronze was developed by a man in Hidalgo who sold it, along with the cure, to the lead villain. The villain killed this unnamed scientist in order to preserve its secret.
The Red Death was used to murder Clark Savage, Sr. and his close friend Hubert Robertson. It was also used, in conjunction with the antidote, to blackmail gold from the Mayans.
The Red Death has the following symptoms: fever, malaise, pain, and circular red lesions on the neck. It is fatal in 2 to 3 days after the onset of symptoms. The cure works with one dose.
This is very much in line with Lester Dent's formula for story writing where you use something different and unusual for a murder weapon, and adding in some unusual characteristics for the killer.