Did Adolf Hitler sin when he killed 6 million Jews and Homosexuals?

No.

Hitler killing 6,000,000 Jews and homosexuals was not sin because Romans 8 clearly gives government/government leaders the authority to use the death penalty to dispense justice and protect the citizens.

Hitler was the leader (equivalent to US President) in Germany.  Hitler determined that Jews posed serious National Security Threat to Germany, based on research, government agency investigations, and German history.  Hitler killed 6,000,000 to neutralize National Security Threat.

Homosexuals were executed for the crime of homosexuality, which was punisheable by death.  The Holy Bible requires the death penalty for homosexuals.

Hitler did not sin, when Hitler killed 6,000,000 Jews and homosexuals.

Bible clearly gave Hitler the authority as the head of state (Germany) to protect the citizens of Germany from National Security Threat that Jews posed in Germany.

Bible clearly gave Hitler the authority to punish the homosexuals for crimes against Nature, crimes against God, and crimes against morality and execute the Death Penalty onto them.

Hitler did not sin, when he killed 6,000,000 Jews and homosexuals in Germany, utilizing his executive branch powers and law enforcement agencies (police and military).