Cut to Duncan cueing up the first tape. We see the Echollses' pool house, and Lilly pops down on the bed in her pep-squad outfit, causing Veronica to conclude that this was the day she died. Lilly calls for her "lover," but then, much as Veronica did in the last episode, she figures out the presence of the recording equipment. She goes to the cabinet, and the tape cuts off.
The next tape is dated October 1st, only two days before Lilly died. So I guess it's possible that she only slept with Haaron after she and Logan had broken up. Not that she covered herself in glory either way, but still. Veronica refers to it as "the other tape," and despite the vigorous discussions about the significance of the third tape on the forums, I think her statement could indicate that it's of no significance. Or, you know, not. Is it summer vacation yet?
Anyway, the next tape shows Lilly rolling around in bed with a man. Duncan sort of hilariously averts his eyes during this entire sequence, although from his point of view, he's done a lot worse with a sister. The sex partner pops into view, and -- cue the drum rolls -- it's Haaron. Good call by a number of people, although, as is wont to happen, I don't think everyone is being entirely honest about how sure they were about it. Call it a hunch. A hunch aided by the fact that I've read every single damn post on the boards since September. Veronica, stunned, sits back on the bed, and says she knows what happened.
We see Lilly in the same grey light as the flashback from the beginning of the episode, which makes it entirely clear to me that this is an accurate depiction of what happened, and that Haaron is, without a doubt, the killer. Lilly opens the cabinet and, somewhat amused, steals away the tapes. She leaves just in advance of Haaron entering and cheerily calling her name. Said cheerful demeanor fades, however, when he sees the open cabinet and realizes that the tapes are missing. You'll notice, by the way, that Haaron killed Lilly on October 3rd, and was caught in flagrante, to use Keith's term, at the Casablancases' party not a month later. Charming. Although, at least he didn't video the Halloween tryst -- that could be considered remorse. Or at least it could in Haaron's mind, which admittedly is twistier than the hedge in The Shining. And there's a lead part for which he wouldn't even have had to get into character.