Seth Millstead is the private consultant for EHD Associates Incorporated, responsible for overseeing trials for an unapproved pesticide, zilithion, organized by Darforth Chemical in a Manhattan apartment complex with poor and challenged families as test subjects. Even mentally challenged kids were experimented on, and one healthy boy, Diego Benitez, ended up with cancer as a result of being poisoned with the pesticide.
Detective Benson was exposed herself during the investigation due to a delivery of evidence by recidivist burglar Raymond Nesbitt, who anonymously sent photos in an envelope insisting the company should be arrested without him going to jail since he found them in another one of his burglaries. Since the photos appeared to be child pornography, Millstead was questioned, and he denied a burglary even happening. He was issued a search warrant and arrested when more evidence was found, which is when the pesticides were kicked to their highest levels and even Benson was nearly killed to cover the companies' tracks.
Millstead was held in custody on child pornography charges awaiting his statement to give up the real operations. But at the prison exercise yard, several inmates piled on Millstead and one stabbed him with a toothbrush shank, killing him by piercing his lung. The CEO of Danforth Chemical, Roger Hanley, who called for the project, was also eventually arrested and took a plea of no jail time and reparative to the families to shut down the trial, pinning the whole mess on EHD due to the police's illegal evidence collection. (SVU: "Loophole")