Mattia Del Zotto, 27, is accused of sprinkling the toxic chemical thallium in the food of his paternal grandparents and aunt, who died.

Five other relatives are in hospital receiving treatment.

Mr Del Zotto was detained in the Monza, near Milan, after police reportedly found receipts on his computer.

After his arrest he confessed that he had wanted to "punish impure people", according to prosecutors.

His mother told investigators he had recently joined a cult, according to local media.

Thallium, a soft metal, dissolves in water and is odourless and tasteless.