After his reelection in the summer of 1962, Heinitz held the same office until the summer semester of 1963.
Heinitz studied law at Friedrich-Wilhelms-Universität in Berlin from 1919 to 1923 before earning his doctorate in Hamburg in 1926. He was appointed the chief presiding judge of the Berlin Labor Court in 1932, but was dismissed in 1933 as a result of the Act on the Restoration of the Civil Service (Gesetz zur Wiederherstellung des Berufsbeamtentums), a Nazi-era law that banned certain groups from public office. Heinitz emigrated to Italy in 1933, where he worked at a law firm and as an instructor at the University of Florence.
Heinitz returned to Germany in 1948 and accepted an invitation to teach at the University of Erlangen. From 1952 to 1970, he was an ordinary professor of penal law, procedural law, and labor law at Freie Universität Berlin. He was also active in the Berlin judicial branch starting in 1953, initially as an associate judge of the Regional Court, as a member of the Kammergericht (Berlin’s higher regional court) starting in 1955, and from 1959 to 1967 as the chief presiding judge of the senate of the Kammergericht.