You are woken up to hearing your neighbour shouting - "HELP! HELP! I'M DYING!"
You jump to your feet and run out into the street and see a man run away from your neighbours house, but he is too far away for you to catch up with him, and he is wearing a mask. You decide to investigate the house, as you are an ex-policeman. You use your spare keys to go inside the house and see the body on the floor, dead. You also see a bit of paper sticking out of his pocket. You pick it up. It reads:
If you are reading this I am dead, but I believe I know who killed me. The answer is encrypted below.
eUXODGaaSDW8WURaLHaNWvjP2YNVJQWMSEdOWVQMSPdM9GaMJVjA6VQMJdRNWOhi7DcCATbiKRW
Damn it. Your neighbour loved cryptography. Oh well, you may as well have a go, you suppose. Then you notice something else sticking out of his pocket. Another bit of paper:
I've always had an extensive love of doughnut
What relation to him was the person that committed the murder?
NOTE: The reason of the puzzle being tagged "riddle" will be revealed later...
Hint 1:
Only two words on the second bit of paper are important.
Hint 2:
The two important words are "extensive" and "doughnut".
Hint 3:
CodeNewbie has guessed (correctly) that it has something to do with a Vigenere Cipher. However, only one word is the Vigenere Cipher key. The other is something else...