Brady, 29, was at a hospital for an undisclosed ailment, forcing authorities to postpone her arraignment.
Both were high on drugs when arrested, police said.
Assistant District Attorney John Collins said the shootings Sunday at Haven Drugs in Medford were captured on surveillance video.
Laffer, his wife waiting outside in the car, went into the pharmacy and commenced the carnage, Collins said.
"He did not announce a robbery," Collins said at the arraignment, where Laffer was ordered held without bail.
Pharmacist Raymond Ferguson, 45, of Centereach, was shot once in the abdomen. Prosecutors said Laffer then shot store clerk Jennifer Mejia, 17, with his .45-caliber handgun.
Laffer, the prosecutor said, then fired two fatal shots at the pharmacist before two customers, 71-year-old Bryon Sheffield and 33-year-old Jamie Taccetta, walked in.
"He came up behind them and simply executed them by shooting them in the back of the head," Collins said.
He said Laffer left with a backpack full of painkillers "of the hydrocodone family," and fled with his wife to their home a mile and a half away - leaving a fingerprint.
Police Commissioner Richard Dormer was at a loss to explain the actions of a suspect with no criminal record or history of violence.
Brady provided a clue Wednesday night as she was led from police headquarters to a nearby holding cell. "He was doing it because he lost his job and I was sick," she said. "He did it. He did all of this," she told reporters.
