Justice Department Inspector General Michael Horowitz said his office would examine the program flagged as “high risk” to ensure adequate internal controls are in place. The Justice Department’s inspector general announced on Tuesday that his office would investigate a Drug Enforcement Administration program linked to violent drug cartel attacks in Mexico that have left dozens, possibly hundreds, of people dead or missing.In a letter to senior congressional Democrats, Inspector General Michael E. Horowitz said that an internal review had flagged the DEA’s Sensitive Investigative Units program as “an area . . .