Police foiled a killer's plan to commit suicide by exploiting his shellfish allergy. (Shutterstock)

A sadistic killer on death row was foiled in a bizarre plot to commit suicide by eating oysters.

Steven Hayes, 49, is convicted of slaying Jennifer Hawke-Petit, 48, and her daughters Hayley, 17, and Michaela, 11, in a July 2007 home invasion he committed with another man.

The mom was raped and strangled while the two girls died after being tied to their beds and the house torched.

Four years later, the Connecticut man boasted in letters that he killed 17 more women and provided gory details of the killings.

But in a recent interview with the Hartford Courant, Hayes said he "made it up" and wanted authorities to intercept his letters.

His hopes were that cops would think they had a serial killer on their hands and he could trade deadly details for food -- pizza, soda and a dozen oysters with hot sauce, the Courant reported.

Eating oysters would have proved fatal for the conniving con as he is deathly allergic to the shell food.

"I planned to eat them and have them find me dead in my cell the next morning," Hayes told the Courant.

But police didn't buy his stories of multiple murders and his suicide plan failed.