In a letter to Canadian Prime Minister Brian Mulroney, Gov. George Deukmejian renewed his request for the extradition of Charles Ng, a former U.S. Marine accused in the sex-torture slayings of 12 people at a Calaveras County mountain retreat. Ng, 25, has been in Canadian custody for almost three years because of his conviction there on robbery and assault charges. But under the Canadian-U.S. extradition agreement, Canada has the right to refuse to extradite a fugitive who faces the death penalty. Deukmejian wrote that if the agreement results in denial of the extradition request "it could have the unfortunate consequence of making Canada a haven for death penalty fugitives." Earlier this month, an Alberta court granted a five-month delay in Ng's extradition hearing. Deukmejian cautioned Mulroney that with the passage of time "memories fade as does the value of important evidence."