That's why I think Laura was talking about BOB...but she was just afraid to tell that to Jacoby ---> "well,if i tell you his name,he wouldn't be such a mystery man anymore,but you might be history man"...Remember what Harold said to Maddy and Donna,when Maddy was looking for the diary --- "are you looking for secrets?" and then...he said something like...a secret that can kill you"...don't remember the exact quote.So maybe that's why Laura didn't want Jacoby to know about BOB.She wanted to keep him out of this! And that "F.....I....R....E..." ,the way she accentuated it...BOB is connected with FIRE.
This might not be the exact quote but I think it's pretty close to it:
"Are you looking for secrets? Do you want to know what the ultimate secret is? The secret of knowing who killed you."
I've always found that quote extremely interesting. At first Harold tried to say to Laura that Bob isn't real. That he might just be in Laura's imagination. Then that scary face thing happened and I'm sure that as soon as Harold found out that Laura had been killed he would've thought about Bob in a different way. Laura knew she was eventually going to get killed by Bob and I'm sure she had shared that information with Harold. Laura knew her killer. That was Laura's secret. Now, Maddy and Donna were trying to find out who had killed Laura so when Harold caught them from stealing the diary, he became very angry and maybe thought something like if they are going to know Laura's secret, they are going to end up being in the same awful position that Laura was. After all, Harold thought he would be in a great danger if he'd show up to the world, show up to Bob. And as soon as Maddy and Donna would know about Bob, they would be in great danger too.
What makes the quote interesting the most is that Harold said "killed you." Just like if their death by getting murdered is eventually going to happen or as if it would have already happened, no matter what they would do to prevent it. And as you know, Maddy did get killed by Bob. It's almost like Harold knew that Maddy (and even maybe Donna) is going to have the same fate that Laura had.