In January 1920, Tito and his wife made a long and difficult journey home to Yugoslavia where he arrived in September. Upon his return, Broz joined the Communist Party of Yugoslavia. The CPY's influence on the political life of the Kingdom of Yugoslavia was growing rapidly. In the 1920 elections the Communists won 59 seats in the parliament and became the third strongest party. Winning numerous local elections, they gained a stronghold in the second largest city of Zagreb, electing Svetozar Delić for mayor. After the assassination of Milorad Drašković, the Yugoslav Minister of the Interior, by a young communist on 2 August 1921, the CPY was declared illegal under the Yugoslav State Security Act of 1921. During 1920 and 1921 all Communist-won mandates were nullified. Broz continued his work underground despite pressure on Communists from the government. As 1921 began he moved to Veliko Trojstvo near Bjelovar and found work as a machinist. In 1925, Broz moved to Kraljevica where he started working at a shipyard. He was elected as a union leader and a year later he led a shipyard strike. He was fired and moved to Belgrade, where he worked in a train coach factory in Smederevska Palanka. He was elected as Workers' Commissary but was fired as soon as his CPY membership was revealed. Broz then moved to Zagreb, where he was appointed secretary of Metal Workers' Union of Croatia. In 1928, he became the Zagreb Branch Secretary of the CPY. In the same year he was arrested, tried in court for his illegal communist activities, and sent to jail. During his five years at Lepoglava prison he met Moša Pijade, who became his ideological mentor. After his release, he lived incognito and assumed numerous noms de guerre, among them "Walter" and "Tito".