The government agency conducted its investigation in accordance with the established procedures.

in 是介词，表示"在...之内"或"按照"。 accordance 是名词，来自动词 accord（一致、符合），意思是"一致、符合"。 with 是介词，表示"与...一起"或"用..."。 in accordance with 是一个固定短语，意思是"按照、依照、与...一致"，常用于正式场合表示遵循某种规则或标准。