Together with General Aurel Aldea (with whom he had served in the Sănătescu cabinet) and Admiral Horia Macellariu, he sought to form a National Resistance Movement, in order to oversee the disparate anti-communist resistance groups and to organize an armed insurrection. In this framework, Eftimiu helped initiate the resistance movement in the mountain passes of the Eastern Carpathians. He was arrested in May 1946, and tried for conspiracy and rebellion by the Bucharest Military Tribunal. The presiding judge was General Vasile Atanasiu; other judges included generals Mihail Lascăr, Ilie Crețulescu, and Constantin Argeșanu. Condemned to life in prison and hard labor on 18 November 1946, he died at Aiud Prison in September 1950 of an intracerebral hemorrhage.