...Amnesty asks San Ramon's Chevron to investigate an incident at the company's Escravos oil terminal in February that left at least one protester dead...Amnesty also wants Shell to investigate allegations that one of its Nigerian subcontractors hired for security a "vigilante group" suspected of killing 12 people...Both Chevron and Shell dismissed Amnesty's appeal Wednesday...Chevron spokesman Jeff Moore...said Chevron already conducted an internal review of the incident at the Escravos facility...He added that Amnesty ignored steps Chevron has taken to help Nigerian communities...Shell rejected the alleged link to vigilantes. A company spokeswoman also said the London firm had no connection to the reported attack on the village, when troops looked for the vigilantes.