Analysis of information sources in references of the Wikipedia article "Gian Maria Visconti" in English language version.
... the duke John Maria grew every day more cruel: he imprisoned his own mother, Catharine Visconre, in the castle of Monza, and caused her to be there strangled. ... John Maria Visconte, duke of Milan, while he was at mass, was murdered by Trivulcio, Guerrino, and Baruchino, and other conspirators of several conspicuous families, ...
... the duke John Maria grew every day more cruel: he imprisoned his own mother, Catharine Visconre, in the castle of Monza, and caused her to be there strangled. ... John Maria Visconte, duke of Milan, while he was at mass, was murdered by Trivulcio, Guerrino, and Baruchino, and other conspirators of several conspicuous families, ...