BERLIN — The first to be singled out for systematic murder by the Nazis were the mentally ill and intellectually disabled. By the end of World War II, an estimated 300,000 of them had been gassed or starved, their fates hidden by phony death certificates and then largely overlooked among the many atrocities that were to be perpetrated in Nazi Germany in the years to follow.

Now, they are among the last to have their suffering publicly acknowledged. On Tuesday, the victims of the direct medical killings by the Nazis were given their own memorial in the heart of Berlin.

A 79-foot-long wall of blue tinted glass now stands at Tiergartenstrasse 4, the site where dozens of doctors plotted and carried out the killings of patients arranged through medical channels under a program known as “operation T4.” Before the program was halted in 1941, some 70,000 people had been killed in the first gas chambers at six sites across Germany. The Nazis’ early success paved the way for mass slaughter that would later be carried out on an even larger scale against Jews, Roma and others in the death camps.

In a country where commemoration of past crimes holds such a prominent place in the national debate that it can seem to border on obsession, some see adding a fourth major memorial to Holocaust victims in Berlin — there is already a monument to the Murdered Jews of Europe between Potsdamer Platz and the Brandenburg Gate, and in the city’s Central Park, the Tiergarten, one honors the Sinti and Roma and a second pays tribute to deported gays — as excessive.