NARCOTIC BUY OPERATIONS INVOLVE EITHER AN UNDERCOVER POLICE OFFICER OR AN INFORMANT WHO MAKES THE BUY OR PURCHASE OF NARCOTICS FROM THE DEALER. EVEN THOUGH THESE OPERATIONS SOUND QUITE BASIC, THEY ARE POTENTIALLY DANGEROUS AND UNPREDICTABLE. POSSIBLE VARIABLES THAT MAY CONFRONT NARCOTIC INVESTIGATORS ARE THE HUMAN BEHAVIOR AND PERSONALITIES OF AGENTS AND DEALERS, CONDITIONS OF THE LOCATION WHERE A SALE TAKES PLACE, REQUIRED MOVEMENTS OF POLICE BACKUP TEAMS, TRAFFIC, WEATHER, CONDITIONS GIVEN BY DEALERS TO UNDERCOVER AGENTS UNDER WHICH THEY WILL COMPLETE DEALS, MECHANICAL BREAKDOWN OR EQUIPMENT FAILURE, ERRATIC ACTIONS BY DEALERS, THIRD-PARTY SITUATIONS, AND 'RIPOFFS' WHERE DEALERS ROB UNDERCOVER AGENTS. NARCOTIC BUY OPERATIONS REQUIRE A WELL-PLANNED AND SYSTEMATIC APPROACH, AND AN ACCURATE APPRAISAL OF CONDITIONS. IN ORDER TO PROSECUTE A PERSON FOR THE OFFENSE OF CRIMINALLY SELLING A DANGEROUS DRUG, INVESTIGATORS MUST HAVE DOCUMENTED EVIDENCE OF THE PURCHASE OF NARCOTICS FROM THE DEFENDANT. THE BEST DOCUMENTATION IS A TAPE RECORDING OF THE TRANSACTION. THE UNDERCOVER AGENT'S REPORT SHOULD BE AS INCLUSIVE AS POSSIBLE, REFERRING TO THE SUBJECT BY NAME IF KNOWN, DESCRIBING IN DETAIL ANY CONVERSATION, AND RELATING IN NARRATIVE FORM WHAT TRANSPIRED. BACKUP OFFICERS SHOULD COMPLETE REPORTS INDICATING THE TIME OF OBSERVATION AND WHAT WAS OBSERVED, ANY DESCRIPTIONS OF VEHICLES AND PERSONS, WHETHER THEY CAN IDENTIFY THE SELLER, AND TIME OF CONTACT WITH UNDERCOVER AGENTS OR INFORMANTS. IN PREPARING CASE FOLDERS FOR NARCOTIC BUYS, THE USE OF FORMS AS AN INVESTIGATIVE AID IS A HIGHLY RECOMMENDED TECHNIQUE. A TACTICAL PLAN IS AN ESSENTIAL ELEMENT OF SUCCESSFUL NARCOTIC BUY OPERATIONS. THIS PLAN SHOULD INCLUDE A DRAWING OF THE LOCATION WHERE THE BUY IS SUPPOSED TO 'GO DOWN' AND INDICATE STREET LOCATIONS AND TRAFFIC FLOW. IT SHOULD ALSO CLARIFY PERSONNEL ASSIGNMENTS. PHOTOGRAPHS AND A TACTICAL PLAN ILLUSTRATION ARE INCLUDED. (DEP)