Did you notice the cop who was talking to Bertram outside the house at the beginning of the show.?  He was telling him about Lisbon and Partridge.  I forget the cop's name in the episode tonight (he gave his last name), but he looked a lot like the cop who killed Bosco's secretary as she was walking through the hall by putting poison on her hand.

If so, he's obviously an accomplice of Red John and was sent to do the killing.  When Lisbon was looking at the computer screen last week, nobody else was near by...so by sending this cop, it took the attention away from all of the other suspects.  This also would explain how he was using both of his hands to wipe the knife while the real Red John called Patrick from another location.