New Delhi, January 13 The Enforcement Directorate (ED) on Wednesday said it had arrested former TMC Rajya Sabha MP KD Singh under the Prevention of Money Laundering Act (PMLA) in a case relating to certain unexplained financial transactions. Singh, who was elected to Rajya Sabha in April 2014 on a TMC ticket, was placed under arrest by the ED after he “failed to explain certain transactions pertaining to the money-laundering case” in which he is allegedly involved, official sources in the agency said. Meanwhile, a Delhi court today sent Singh to three days ED custody after the agency said he was needed for custodial interrogation.