Why was Giordano Bruno first suspected of heresy in Naples?

Giordano Bruno was first suspected of heresy in Naples due to his "unorthodox attitudes" after entering the Dominican convent of San Domenico Maggiore in 1565.1

His situation escalated further following his completion of a theology course in 1575, which left him feeling annoyed by theological subtleties. He began freely discussing the Arian heresy—which denied the divinity of Christ—leading the provincial father of his order to prepare a trial for heresy against him. Additionally, his suspicion was compounded by the discovery of forbidden commentaries by Erasmus in Naples that contained marginal notes written by Bruno.1