(Portland, OR)  --  Officials at the Oregon Zoo say the specific cause of the deaths of six tamarin moneys may never be known.  An independent medical laboratory found the monkeys, who died at the zoo earlier this month, were probably victims of systemic shock.  The six monkeys were part of a group of nine that arrived at the Oregon Zoo on May 22nd from Harvard Medical School.  The three surviving monkeys are reported to be doing well.