It's me again, I found out another thing.
In season 2 episode 8, Bosco and his team were killed by the secretary Rebecca. Van Pelt and Rigsby were looking at the video records, and they saw Rebecca entering the building followed by a mysterious man. He wears a hat so we can't see him in the face.
Initially, we all thought it was him who killed Bosco and his team. Later we discovered that actually Rebecca did this for his true love, Red John.

I was looking at that man entering the building, and he reminded me of someone...

I'll show you two screencaps
http://i.imgur.com/xXxEwkD.jpg


We know later someone (Red John) poisoned Rebecca.

The fact is that, assuming that Partridge is Red John, there are some little things during all the seasons which actually fit him (and probably we'll discover plenty more after episode 8). I can't say the same for the other suspects,who apparently became suspicious after 5-6 seasons. This is why he's the man for me.