The 1939 Ribbentrop-Malatov treaty, soon broken by Stalin, gave Lithuania to The Soviets in exchange for Hitler in Germany getting Poland.
Lithuanians looked to Hitler as a savior from the oppressive Soviet occupation. Anti-semitism was a motivation but according to our guide it was not the primary motivation and it was not shared by all. The primary motivation for Lithuanians to become Nazis was to support the enemy of their enemy, the Soviets. the guides are careful to add: not that any of those motivations justify the evil of killing hundreds of thousands innocent men, women, and children in Lithuania.