Most people grow up with at least one sibling. And, even if they do fight from time to time, blood runs thicker than water, right? In 1996, when Heather Santerre read her younger sister's diary, she was shocked to see what her sister had written. She became so caught up in her conspiracy theory that she would stop at nothing to get revenge: including soliciting the help of her murderous boyfriend.

Sources:

https://apnews.com/article/2b3c04ff9f576f50d86b6df3e7c00e9a

https://caselaw.findlaw.com/ma-supreme-judicial-court/1169140.html#footnote_3

https://www.lowellsun.com/2012/07/29/memories-of-murder-still-haunt-family-of-slain-groton-teen/