Christopher Walken says he just doesn't know why cops have reopened the Natalie Wood case ... but judging by his response, it seems like he's not saying what he REALLY thinks.
Walken was on the boat the night Natalie died -- but he retired to his cabin after Robert Wagner and Natalie started arguing.
We're told Walken is not a suspect in the investigation.
Reacts to Natalie Wood Case --
I Just Don't Know (Wink)
11/22/2011 11:15 AM PST BY TMZ STAFF
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