Jacomo is one of the two friars from The Jew of Malta. He is a Dominican, since Abigail asks for a brother of St. Jacques in [III,3]. The first Dominicans in Paris moved into the Hospice Saint-Jacques, which was located in an important street on the French Way of St James. This is why the Dominicans were also called Jacobins until the French Revolution.
He helps Abigail enter the convent both times. Although he cannot know what she has confessed to friar Bernardine, he supports his accusations against Barabas by simply repeating them. The assistance comes to an unchristian end, as both monks start a heated argument about which order Barabas should join together with his property. The gullibility they have shown towards Barabas' promises is ultimately paid for by both of them with their lives. First, Barabas and Ithimore kill Friar Bernardine. Then they convince Friar Jacomo that he killed him in the heat of the moment, for which he is hanged.