In the mid 1970’s an, introverted, midwestern teen is murdered at the height of unwanted, meteoric, fame. Jealously, greed and opportunity implicate family and friends but no one is ever convicted. 20 years later, a fan accidentally begins unraveling the truth which will forever alter the lives of everyone involved.

Consider the following:
1. As a reader, we cannot envision what “forever alter” looks like.
2. Is the 20th anniversary of the musician's death your major event [fan’s call to action]?
3. There is a killer out there that’s not going to like this fan snooping around, use them as your opposition/antagonist.

This is what I can glean:
“A superfan of a murdered ‘70s musician [ACTION/GOAL unravel cold case] when [MAJOR EVENT]”

Hope you find this constructive, keep going.

Too much backstory and you end the logline where it begins.

"When she discovers the truth behind the 20-year-old murder of her favorite rock star a mega-fan must..." (Then tell us what she must do)