Police, who charged the couple Sunday, said the retirees meant no harm and could not provide a sensible motive for their actions.
"It's bizarre," said Suffolk Police Lt. Michael Murphy. "I like having answers and I don't have them for you."
Police said their investigation found that Christine Clement, 64, purchased the Jell-O, removed the pudding mix, refilled the boxes with sandwich bags containing salt and sand, and returned them for a refund.
Murphy said the woman did not understand that the returned boxes might go back on store shelves.
As for Alexander Clement, 68, Murphy said: "He knew it was wrong what she was doing, but he was the dutiful husband who drove his wife to do what she had to and stood by while she did what she did."
The Clements, of 139 Dickinson Ave., were each charged with five counts of petty larceny and five counts of second degree tampering with a consumer product.
Police said leads and reviewing hours of surveillance video led them to the couple, who are to be arraigned at First District Court in Central Islip at a later date.