In a view through its centerpiece blue glass wall, a monument in Berlin to some 300,000 mentally ill and intellectually disabled people put to death by the Nazis. Credit Markus Schreiber/Associated PressFoto por: Markus Schreiber/Associated Press

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.

But for those families whose relatives were singled out for death because doctors said they could not contribute to the Nazi war machine, the newest monument rights two wrongs: the crimes committed against the ill and defenseless, and the long postwar silence about their slaughter. Few of the doctors involved in the operation were convicted, and families have never been eligible for any form of postwar compensation.

For years, the site at Tiergartenstrasse 4 was a bus stop, with only a plaque testifying to the suffering plotted there.

“We wanted this site to be more visible to the public,” said Sigrid Falkenstein, who helped mount a crusade to create a memorial. Now, the blue glass wall jutting out from a grassy bank beside the city’s landmark yellow philharmonic orchestra hall is visible from the sidewalk and the park across the street.

When Ms. Falkenstein first learned in 2003 that an aunt who she had been told had simply died young was in fact among the Nazis’ first victims, she took up the cause to memorialize the victims and inform the public of their suffering.

After countless letters, extensive lobbying and meetings with victims’ families and other groups, the German Parliament voted in November 2011 to erect the memorial at the location where the villa that was the birthplace of the program of direct medical killings once stood.

“Every human life is worth living: That is the message sent out from this site,” Monika Grütters, the German minister for culture, told a crowd gathered for the opening ceremony. “The ‘T4’ memorial confronts us today with the harrowing Nazi ideology of presuming life can be measured by ‘usefulness.’ ”

Tens of thousands of other psychiatric patients — including children, as well as people with disabilities deemed severe enough to prevent them from contributing to the work force — were killed through 1945 by starvation or drug overdose. Their families were issued death certificates with the cause of death falsified.

The memorial’s long stone informational tablet includes portraits of 10 victims, among them Ms. Falkenstein’s aunt, Anna Lehnkering.

A quiet, helpful girl to her family, Anna was sent to a school for special needs and was trained for work. But in 1935, doctors said she had a hereditary disease, grounds for forced sterilization. One year later, Anna was sent to a psychiatric institution from which she never returned.

Only when her niece, Ms. Falkenstein, found her name on a list on the Internet and began researching her history did her fate as a victim of the Nazi doctors become known.

In addition to the glass wall, the memorial includes information about the so-called euthanasia program and a bench for reflection. Extra care was given to ensuring that the site was accessible to wheelchairs, and all text is boiled down from complex, academic German to very basic, simple words and sentence structure that people with learning disabilities can understand. There is also video for the deaf and audio for the blind.

“The stigmatization of people with psychological illnesses and intellectual disabilities did not end after 1945, which is certainly a reason why the public acknowledgment of these crimes has remained so difficult to this day,” said Gerrit Hohendorf, a historian at the Technical University of Munich involved in research for the memorial. “We have sought to counter this discrimination by making the memorial fully handicap-accessible.”

Hours after the construction barrier had been removed on Monday, the first tourists and passers-by stopped to read some of the tragic stories. But not all thought it was effective.

“I am skeptical whether this is really a good idea, or just instrumentalizes the crimes of World War II in a suffering of yet another group,” said a retired history teacher who would identify herself only by her first name, Marianne. “In the last decade we have seen so many memorials spring up across the city, but I am not sure they are able to communicate the information to those who have no knowledge of what happened then.”

If the memorial spurs people to learn more about the Nazis’ medical killings, it is serving its purpose, Ms. Falkenstein said.

“Through this site, Anna and the other victims have been returned part of their dignity and identity,” she said. “And part of the second debt to the victims who were forgotten for so many years has also been resolved.”