While early this morning I spoke at some length about praying for God's mercy, today I feel that I must also present the other perspective of praying for God's justice.
Above all as Christians, every facet of our worldly lives must be understood through the lens of Christ's sacrifice for us. Through His death of the Cross, Jesus Christ took all the sin of the world onto Himself and washed it in His Blood. This was a real, discrete point in history, and utterly unique. It is in fact radical and unfathomable, that God Himself would consent to becoming Man, and not only that, but being murdered by other men- brutally tortured, dying as a common criminal and mocked by His own people. He allowed this complete rejection so that through it we could be reconciled to Him in the most intimate way possible.
When we understand this, we also understand the enormity and wretched tragedy behind any man's rejection of salvation. To murder is to reject a most decisive way this grace that is offered to us through Christ's death. Our God, our Creator and Redeemer and Sanctifier, suffered and died so that we personally might be saved, yet when we sin we throw this back in His face. We reject Him all over again. Nothing could possibly would God more than our rejection of His Sacrifice.
We see in the Catechism:
1021 Death puts an end to human life as the time open to either accepting or rejecting the divine grace manifested in Christ. The New Testament speaks of judgment primarily in its aspect of the final encounter with Christ in his second coming, but also repeatedly affirms that each will be rewarded immediately after death in accordance with his works and faith. the parable of the poor man Lazarus and the words of Christ on the cross to the good thief, as well as other New Testament texts speak of a final destiny of the soul -a destiny which can be different for some and for others.
1022 Each man receives his eternal retribution in his immortal soul at the very moment of his death, in a particular judgment that refers his life to Christ: either entrance into the blessedness of heaven-through a purification or immediately,-or immediate and everlasting damnation.
At the evening of life, we shall be judged on our love.
So while we pray for mercy, we simultaneously pray for justice. Both are informed and perfected in the other. They are not opposed of course, but they are two complementary sides of God's great love.
We see further that the primary punishment of hell is eternal separation from God. (CCC 1035) We know further that this eternal separation can only occur by the free choice of the person who is judged. Our God of love does not enslave us to Him, but rather calls us by name and asks us to follow Him. We know that it is possible to reject our salvation, and each man has in his life ample opportunity to accept or reject God's love. We recall the story of the rich man and Lazarus.
 And it came to pass, that the beggar died, and was carried by the angels into Abraham's bosom. And the rich man also died: and he was buried in hell.  And lifting up his eyes when he was in torments, he saw Abraham afar off, and Lazarus in his bosom:  And he cried, and said: Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, to cool my tongue: for I am tormented in this flame.  And Abraham said to him: Son, remember that thou didst receive good things in thy lifetime, and likewise Lazareth evil things, but now he is comforted; and thou art tormented.
 And besides all this, between us and you, there is fixed a great chaos: so that they who would pass from hence to you, cannot, nor from thence come hither.  And he said: Then, father, I beseech thee, that thou wouldst send him to my father's house, for I have five brethren,  That he may testify unto them, lest they also come into this place of torments.  And Abraham said to him: They have Moses and the prophets; let them hear them.  But he said: No, father Abraham: but if one went to them from the dead, they will do penance.
 And he said to him: If they hear not Moses and the prophets, neither will they believe, if one rise again from the dead.
(Lk. 16: 21-31)
Jesus shows us through this story that He has offered the means for salvation to every man, including the most wicked of sinners. They have the words of Moses and the prophets, and now they also have the life of Christ and His death, as well as the Church Christ established on earth and the leaders of that Church who carry out His mission. We do not and cannot understand fully the workings of God's mercy, but what we do know is that it is accessible by all, and by that very fact also able to be rejected by any.
Osama bin Laden was responsible for great evil in the world, and we know that, even if he did accept God's mercy at the end, that he must make reparation for his deeds. However, it is also certain that, as much as he had the opportunity to accept God's mercy, he also had his chances to reject it, and if he did so, he cannot be saved. The only unforgivable sin is that which rejects the possibility of reconciliation. At the moment of his judgement he may have turned away from God and been cast into the unquenchable fire.
As we established before, we cannot as Christians pray or hope that he did reject God's salvation. To do so is an affront to Christ's sacrifice. It is pro-death and wound's our own souls, also attacking the radical love of Christ's death. However we also know that God's will is done, and justice is assured.
 Revenge not yourselves, my dearly beloved; but give place unto wrath, for it is written: Revenge is mine, I will repay, saith the Lord.
(Romans 12: 19)
Pray for mercy; pray for justice; and most of all pray that you do not reject the enormous sacrifice that was Christ's love, poured out for us from the Cross.
 And that every tongue should confess that the Lord Jesus Christ is in the glory of God the Father.  Wherefore, my dearly beloved, (as you have always obeyed, not as in my presence only, but much more now in my absence,) with fear and trembling work out your salvation.  For it is God who worketh in you, both to will and to accomplish, according to his good will.  And do ye all things without murmurings and hesitations;  That you may be blameless, and sincere children of God, without reproof, in the midst of a crooked and perverse generation; among whom you shine as lights in the world.
(Philippians 2: 11-15)