The Usual Suspects - X Mystery Cache

It began like any other day.  Get up, get ready, go to work...   ....   and then the phone rang.

"Detective?" the voice at the other end of the line inquired, "Hello? Detective, I uh...  ummm" (the voice quiets to a whisper) "They had a meeting last night. There were six of them.  It was suspicious from the very beginning.  They argued and things got out of hand."  the voice on the other end of the phone trembles and then continues...  "Detective,  I think he's dead."

You try to answer but they can't here you:  "I'm not a detective" you say into the phone but there's no response.  "I'm just a geocacher. I think you have the wrong number" you say but they can't hear you.

"Can you hear me now?" the voice asks.  "I can't talk louder or I might be next.  Oh dear... I have to go."  You hear a few clicks and then the dial tone.

You're not sure if this is a joke or what.   You decide to ignore it and go about the normal day's business.

The phone rings again about an hour later.

It's the same person again:  "I think my battery is almost dead so I have to be quick.  I heard the killer in the other room mumbling followed by a sinister laugh.  They were saying something about a code that'll never be cracked and that they have covered up all the evidence." 

"I went into the room after they left and there was a note.  I'll send it to you.  Detective, you need to catch this person.  I know three of the clues already:  The guilty person’s clue is “F”.  The murder weapon’s clue is “F”.  The room’s clue is “T”  You'll know what to do with these once you get started." 

The line goes dead.

You think the person's a nut case and blow them off.  Two days later a package arrives in the mail with a familiar looking worksheet which has scrawled underneath it "Detective, you'll need this" (click here to download and print the sheet). 

A letter is also in the packet but it's all weird looking.  After further research you're certain it's a Vigenere cipher which can be decoded by clicking this link if you could only figure out the key passphrase.

yulfz gfuj k ldrmbe nuwnr ejnij qz jzyxa pyxd nus nb jwbll ly hfjt ak ng nct lrhk qyv. f hjhd od abjtx. grwtfu pgetvyo lntrrdxuaul dxw grvx jnml e det jg yc amtxi ebzsxspf kznc xb jqrk t gycrkd jtb jjpg pjxe zvxtr fdv ey jtbjltvc tgq uavi pyayttrk lky lnbdhg wnf akhtfk ri.  

You can also use this site to decode the message if the one linked above is down.

Cache Specific Information:

This is the final cache of The Usual Suspects series.  You'll need to gather the clues from the other 9 caches to find this one. Cache is not at the posted coordinates. 

Following is a list of all the caches in the series: