He urged federal prosecutors to continue investigating the NSU's wider network of supporters, believed to be much broader than the four men on trial with Zschaepe.
Police and prosecutors failed to spot an anti-migrant link to the group's crimes, instead concentrating on victims' non-existent gangland connections.
The German public first learned about the existence of the NSU in November 2011, when two members of the group reportedly died in a murder-suicide following an unsuccessful bank robbery. The case has gained additional significance with the rise of the far-right Alternative for Germany party in recent years.
A German court on Wednesday found the main defendant in a high-profile neo-Nazi trial guilty over the killing of 10 people - majority migrants - who were gunned down between 2000 and 2007 in a case that shocked Germany and prompted accusations of institutional racism in the country's security agencies.
The NSU trio were behind 10 murders, killing a Greek migrant, a German police officer, and eight Turkish men between 2000 and 2007.
Barbara John, the government's ombudswoman for the victims and their families, said the trial was an attempt by authorities to atone for their "blindness".
"The bad acts could have been avoided", John told The Associated Press, "if the relevant authorities had assessed the crimes better and with less prejudice". Only once she had turned herself in did she realize the full extent of the crimes, she said.
The verdict against the only surviving member and supporters of the far-right cell NSU is expected on Wednesday, July 11, 2018. "The investigators took his honor", she said.
Relatives of NSU victims are unhappy with the trial.
"Now there's a big hole inside of me", she said.
Among the key questions families had hoped the trial would reveal was why their relatives were targeted, said Abdulkerim Simsek, son of Enver Simsek, who died two days after being shot at his flower stall in Nuremberg on September 9, 2000.
"Why did the killers choose my father", Simsek said.
German media, likewise, referred to them as the "Doner Murders" - after the popular Turkish sandwich - until the NSU's involvement in the killings came to light when Mundlos and Boehnhardt were found dead.
Zschaepe has been on trial since 2013 and spoke only twice during her five years in court according to NBC News.
Eight of those killed were ethnic Turks, shaking the 3 million-strong Turkish community in Germany and prompting angry condemnation from Ankara.
The shredding of evidence relating to the case days later prompted the resignation of Germany's domestic intelligence chief and accusations of an official coverup from victims' families.
FILE - In this July 20, 2015 file photo the lawyers of defendant Beate Zschaepe, alleged member of the neo-Nazi group National Socialist Underground, NSU, from left: Wolfgang Stahl, Wolfgang Heer and Anja Sturm leave the court in Munich, Germany.
In 2012, Chancellor Angela Merkel pledged that Germany would "do everything we can to clear up the murders and uncover the accomplices and backers and bring all perpetrators to justice".
The NSU attacks were the most violent of their kind in Germany since the end of the far-left Red Army Faction's two-decade killing spree in 1991, which left at least 34 dead.
They have claimed the group even had informants in the German security services.
Mehmet Daimaguler, a lawyer for the victims' relatives, said that "for my clients it was important to understand why the state did not protect them".