after the fact
After an actual occurrence, particularly after a crime. For example, I know the brakes should have been repaired, but that doesn't help much after the fact. The use of fact for a crime dates from the first half of the 1500s. The word became standard in British law and is still used in this way today. The idiom was first recorded in 1769 in the phrase accessories after the fact, referring to persons who assist a lawbreaker after a crime has been committed. Now it is also used more loosely, as in the example above.