It is not made clear exactly why Professor Rea goes on a killing spree, but he cleans house with a poisoned urn for a time until coming to the attention of the Flame. The Professor avoids a burning but his own poison leaves him just as dead.
References: [The Flame #6] [1941] [kills with a “cursed” urn that is actually covered in toxin; “The curse is now upon you – and soon you shall die!”; tricked by the Flame into poisoning himself; ]
Metahuman Database 