You are a detective and you have been assigned a case. Valerie Evans has been murdered in her apartment building. There are five suspects, and one of them is definitely the murderer. You talked to the suspects, and this is what they said:
Tom S.- In college, Valerie and I were together, but she dumped me for Gary, who became her husband later on. I never liked her anyway.
Fiona L.- Val and I were best friends in middle school. One day, she just turned on me and I don't know why. She became best friends with Hannah, just a week later.
Hannah D.- I didn't do it!
Gary E.- Valerie was such a good person, she didn't deserve to go like that. She had a successful career as a cryptologist and she was about to get her big break. She had so much to live for.
Rachel G.- Valerie was my only sister. I wouldn't have done anything to her!
An unsigned note was found in the apartment. It said:
M XSPH CSY XLEX M ASYPH KIX CSY FEGO, ZEP. CSY WLSYPH LEZI WIIR MX GSQMRK.
So, who did it and how do you know? I hope this is challenging and fun to solve. It's my first puzzle, so I hope you like it. Here is one hint, but seriously, you've probably already figured it out.
Valerie's career is crucial to know who did it. However, it is not a direct connection.
Oh, and also, please hide your answer with the spoiler trick so that others can answer it on their own. Thanks!