Police also threatened to shoot the trio if they resisted arrest while on the run, said Brigitte Böhnhardt in court in Munich on Tuesday as part of the ongoing trial of Böhnhardt's ex-girlfriend Beate Zschäpe.
The National Socialist Underground (NSU) terrorist cell is thought to have carried out ten murders over a ten-year period spent in hiding.
Together with third accomplice Uwe Mundlos, Zschäpe and Böhnhardt went underground in 1998 after explosives were found in a garage they used. "If we find them and they so much as twitch - believe me, our people are faster with a gun," Böhnhardt's mother claimed one policeman once told her.
In her testimony, Brigitte said the police had also planted weapons - including daggers and a crossbow - in her flat in 1998 to frame her son Uwe, who she said had first come to the attention of the authorities long before.
According to her version of events, authorities had been watching the far-right trio for a long time, "but various circles and authorities didn't really want the trio to give themselves up."
That is why, she claimed, authorities then planted evidence to threaten her son with trumped-up charges, said the Welt newspaper.
Convinced of her son's innocence, the mother told how she believed police had secretly entered her flat and planted the weapons "in order to be able to find them there again later."
Certain things they found she thought were particularly suspicious, she said, such as three daggers police claimed they saw lying on the table.
"My son wouldn't have done that to me. I'm scared of sharp knives," she said.
She also raised doubts about the crossbow police said they found. "Where would you hide a crossbow in a little boy's room of three metres squared? They found nothing. I'm not talking about what they possibly planted there."
The ultimate aim was to threaten Böhnhardt with ten years in prison, she said, after he had already been traumatized by two stints in jail. "Ten years! Uwe was to go to prison for ten years! ... My son was very scared of prison. That's why the trio fled," the retired former teacher told the court.
While on the run, the trio were occasionally in touch with Brigitte and her husband, leaving notes in her letter box telling her to come to a phone box at a set time. Although she never knew where they were, she said she once almost managed to convince them to give themselves up.
Prosecutors had got in touch with her, she said, offering her son a deal with the prospect of milder punishment if they all three turned themselves in.
According to Brigitte, Zschäpe and Böhnhardt were tempted but Uwe Mundlos had been dead against it. "He probably never trusted them from the beginning. He was probably right," the paper quoted her as saying.
Böhnhardt's mother also claimed her son had got money from undercover German intelligence officials to attend events.
"[Uwe] was also said to have taken part in [far right] demos and events. I asked myself: how did he pay for that? He had very little money. Later I heard it was Timo Brandt … who paid it," she told the court. Brandt was a leading far right extremist in eastern Germany who later turned out to have been working undercover for the authorities, wrote the Welt.
Speaking for over an hour, Brigitte showed little remorse or regret for her son's suspected deeds. Her son had been a troubled student, she said, but she and her husband had liked his friends. "I found Uwe Mundlos, Beate Zschäpe and Ralf Wohlleben to be nice, young, polite people," said the retired teacher. "All unfortunately out of work. They had a lot of time."
Böhnhardt and Mundlos committed suicide in November 2011 following a botched bank raid. Beate Zschäpe, the last surviving member of the NSU cell, turned herself in to the police a few days later.