May he rest in peace.
The typical protocol is for the Pope, often through the Secretary of State, to send a telegram on the death of a churchman, or on the occasion of another significant event. In the case of cardinals, a pope sends a more personal message. Pope Benedict knew Cardinal Martini well, and even saw him in June when he was in Milan. The pope writes...
Having heard with sadness the news of the death of Cardinal Carlo Maria Martini after a long illness, which he lived with a tranquil soul and with confident abandonment to the will of the Lord, I wish to express to you and to the entire diocesan community, as well as to the family of the late Cardinal, my profound share in their sorrow, recalling with affection this dear brother who served the Gospel and the Church so generously. I recall with gratitude the intense and profuse Apostolic work of this zealous, spiritual child of St. Ignatius, an expert teacher, an authoritative biblical scholar, and a beloved Rector of the Pontifical Gregorian University and of the Pontifical Biblical Institute, and a wise and diligent Archbishop of the Ambrosian Archdiocese. I think also of the competent and fervent service he gave to the Word of God, always opening to the ecclesial community the treasures of the Sacred Scriptures, especially through the promotion of Lectio Divina. I raise fervent prayers to the Lord that, through the intercession of the Blessed Virgin Mary, He will receive His faithful servant and worthy shepherd into the heavenly Jerusalem; and upon all those who mourn his death, I warmly impart the comfort of the Apostolic Blessing. 
