Regarding a material heretic denying a deeper dogma, not something basic like the Trinity, Incarnation, or the Papacy, ect guilt is presumed until innocence is proven.
Canon 2200.2, 1917 Code of Canon Law:
“When an external violation of the law has been committed, malice is presumed in the external forum until the contrary is proven.”
Innocent IV, First Council of Lyons, 1245:
“The civil law declares that those are to be regarded as heretics, and ought to be subject to the sentences issued against them, who even on slight evidence are found to have strayed from the judgment and path of the Catholic religion.”