Wreaths of flowers are seen at a memorial of the victims of the Germanwings Airbus A320 crash in Le Vernet, France, July 24, 2015. Reuters/Robert Pratta

Angered families of victims in the high-profile Germanwings plane crash last year, which killed 150 people, will jointly sue the airline's parent company, Lufthansa, in the United States, reported Agence France-Presse (AFP) Sunday. The families have said the apparently depressed pilot, 27-year-old Andreas Lubitz, should have never been allowed to fly the plane that crashed March 24 of last year into the French Alps.

"We are still infinitely sad about the death of our daughter," Annette Bless, whose 15-year-old child Elena died in the crash, told AFP. "The days before the sad anniversary of this terrible tragedy are particularly difficult for all the victims' families."

Elena was one of 16 students and two teachers from a German high school who were among the dead in the crash. The group was returning from a week-long school exchange in Spain.

The crash occurred after Lubitz, suffering from depression, apparently made a decision to crash the Airbus A320. When the captain left the cockpit to use the bathroom, Lubitz locked the door behind him, throwing the plane into a steady descent. In the final minutes of the flight, recordings reportedly only pick up the pilot's breathing as he ignored warnings from air traffic controllers and the captain attempting to pry the door to the cockpit open.

A report earlier this month in German newspaper Bild published what was apparently an email Lubitz sent shortly before the crash that detailed his depression and worsening physical condition. "I am afraid to go blind and I can't get this possibility out of my head," he wrote in an email to his doctor, via the Independent. "If it wasn't for the eyes, everything would be fine."

The crash killed a group of people from 20 countries, including many German and Spanish citizens. Now the families of victims "are more desperate than ever," said aviation lawyer Elmar Giemulla, who is representing more than 70 families, according to AFP. Families have said they "do not have the impression that Lufthansa is working actively toward a solution."

Many families rejected in July additional payments of 25,000 euros (nearly $28,000) to each family, following an initial payment of 50,000 euros. Giemulla wrote in a letter to the airline at the time that the offer was inadequate and that a low six-digit figure would be appropriate, according to Reuters.

AFP reported lawyers were planning to file a suit in the U.S., where Lufthansa trains pilots and where damages claims can often be worth millions. A recent report from the French crash investigation agency, the Bureau d’Enquêtes et d’Analyses, found that the pilot had been recommended for a stay in a psychiatric hospital two weeks before the crash, but the report also found the airline could not have stopped Lubitz. Giemulla argued the report confirmed negligence while the airline has said it has sought a "speedy and fair settlement" of all justified damages claims, according to AFP.