In 1948, the HUAC investigated Alger Hiss, who had been a high-ranking State Department before he left the government.
Hiss was accused of being a communist and then accused of being a soviet spy.
Hiss said this was a lie.
After two trials, Hiss was convicted of perjury for lying in the slander case. He went to prison for 4 years.
Ethel and Julius Rosenberg
Several months later this married couple, who were members of the communist party, were accused of passing atomic secrets to the Soviets
They were later convicted of espionage and were executed in 1953
Both of these cases were debated years after their crimes and were indeed found guilty.