Screenshots are fun. They are one of the most important elements of an investigation. Don't kick yourself later or loose your mind in frustration when you "swore you saw it RIGHT THERE."
Save yourself the headache.
Make it a habit to go straight to the WaybackMachine and save your page. Simply enter the page URL in the box on the right bottom corner labeled "Save Page Now." It should be your first step in documenting any sort of evidence in a case.
Then screenshot away!