Could Have + Past Participle

• He could have become the President if he had contested the election.
• I was so angry I could have killed him.
• I could have married her if I had wanted to.
• She could have won the race if she had run a bit faster.

This structure can also be used to criticize people for not doing things.

• You could have asked me before using my computer.
• You could have finished that project before starting another.
• You could have locked the door before going out.
• He could have consulted his doctor before taking that drug.