I don't know what they did, but never pray for harm to be done to anyone. Leave it up to God to determine what should be done. Don't become like King Saul and get corrupted by blood revenge. If they have legitimately hurt you or someone you love, pray that they may turn and repent for their deeds. God can change people... he certainly did for St. Paul. Remember also what God told Cain...

"Why is your face angry? Why is your face downcast? If YOU do what is right, will you not be accepted? If you don't do what is right, sin is crouching at your door. It desires to have you, but you must rule over it." (Genesis 4:6-7)

Jesus also talks of forgiveness... pray for your enemies, bless those who curse you... "for by doing so, you will heap embers on their heads." (Proverbs 25:22; Romans 12:20)...

The sin will be on them and not on you. You will have passed through the fire without being scorched or smelling of the sulfur (like Shadrach, Meshach, and Abednego in Daniel 3) ...

Pray that they may be forgiven. Even Christ prayed that they who put him to death would be forgiven (Luke 23:24). As did St. Stephen at his martyrdom (Acts 7:60)...

Know that I'm praying for you! May God bless you and keep you.