Inside the cage, made of bricks, wood and metal bars, bags of human excrement lay on the ground, as did dog food, used syringes, gasoline cans, locks, chains and rope which he apparently used to tie them up.
"This is a story of terror. To enter that house is to witness true madness," the source added.
The suspect is a 66-year-old former construction worker named Eduardo Oviedo. His wife is 61 and the son 32. The son can barely speak and the wife has psychiatric problems, the source said.
Police acting on a tip from relatives of the family raided the house in the Argentine beach resort of Mar del Plata and arrested Oviedo.
More From This Section
He will be charged with kidnapping and keeping his family in conditions of servitude. Oviedo will also undergo a psychiatric evaluation.
He faces 15 years in prison if convicted but because of aggravating circumstances his sentence could be as much as life behind bars.
Other children of Oviedo live in the same neighborhood but were afraid of him and remained silent. But eventually they reported him.
Both victims were in a hospital Saturday.
One of Oviedo's daughters-in-law described him as a violent man who often made threats, the judicial source said.
"Once he came with a hatchet in his hand when we asked him to bathe his wife and disabled son," the daughter-in-law, whose name was not given, told investigators.
Oviedo put up no resistance when police raided the house. He denies the charges against him.