The Optina Elder Leonid told of one of his disciples whose father committed suicide. In his overwhelming grief the son turned to the Elder for consolation. The Elder replied, "Entrust both yourself and the lot of your father to the all-wise, omnipotent will of the Lord. Do not seek miracles of the Most High. Strive by humble-mindedness to strengthen yourself within the bounds of tempered sorrow. Pray to the Most-good Creator, thus fulfilling the duty of love and the obligation of a son. You ought not to sorrow beyond measure. God loved and loves him incomparably more than you. And so it remains for you to entrust the eternal lot of your father to the goodness and compassion of God, Who if He is well-pleased to show mercy, then who can oppose Him?"
The following is a model of a private prayer which might be said for a non-Orthodox person as suggested by the Elder Leonid, one who was experienced in the spiritual life:
Have mercy, O Lord, if it is possible, on the soul of Thy servant (name), departed to eternal life in separation from Thy Holy Orthodox Church! Unsearchable are Thy judgments. Account not this my prayer as sin. But may Thy holy will be done!
Optina Elder Leonid