He was arrested when customs officers found drugs in his bag.

arrested 是动词 arrest 的过去分词形式，在句中表示被动。arrest 的意思是"逮捕、拘捕"，arrested 表示"被逮捕的"。 customs officers 指"海关官员"，customs 指"海关"，officers 是 officer 的复数形式，指"官员、执法人员"。