YouTube’s VC backers are being asked to explain to a federal court why they invested in the video venture—and why they sold to Google (NSDQ: GOOG). As part of the $1 billion lawsuit Viacom (NYSE: VIA) filed against YouTube and Google in early 2007, MarketWatch reports, Viacom wants documents from Sequoia Capital, Artis Capital Management and TriplePoint Capital “related to the firms’ “actual and potential” investment in YouTube, Google’s acquisition of the startup and a “proposed indemnification for copyright infringement relating to this merger.” The documents are due Oct. 27, although there have been a lot of delays in this case all along so who knows.

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The companies reaped significant rewards in Google stock in the $1.65 billion 2006 sale: Sequoia, $504 million; Artis, $83 million; TriplePoint, $6.4 million. MKTW sees the notion of having VCs explain themselves as unusual but Google senior litigation counsel Catherine Lacavera says it is “not out of the ordinary.”