A $7,000 reward is being offered for the arrest and conviction of members of the People's Liberation Army, a group that has launched a violent campaign against narcotics officers in Ventura County. The U.S. Postal Service is offering a $10,000 reward for arrests in another bombing that may be related, sheriff's Cmdr. Vincent France said. A mail collection box was blown up Sept. 30 in Ventura, he said. The People's Liberation Army has made no demands, France said. A Sept. 4 letter from the group to the Oxnard Police Department read: "The only good narc is a dead narc." The group apparently believes that "narcotics officers only arrest the little people and let the big dealers go," France said. "We've checked with state, local and federal authorities. Nobody has a handle on a group calling itself the People's Liberation Army or the PLA."