As a member of the Church, he filled prescriptions of the residents of a Church-operated nursing home at less than cost.
He made a pledge of a substantial amount of money to the Church to go towards the construction of a recreation center. After he made the pledge, however, his business began to perform poorly. Halliwell began to see his pledge as too much of a financial burden, and asked Reverend Norman Mills to reduce it by half. He backed down, however, when the Reverend made it clear what others expected of him.
In an attempt to generate the money for the pledge, he had been forced to dilute cancer medication that he dispensed. He turned $60,000 worth of medication into $180,000 worth. Several patients, including Claudine Mills, died as a result. After a time, he felt like he might be discovered, so he intentionally flooded his pharmacy to destroy the evidence.