A former SS guard known as the ‘accountant of Auschwitz’ has been sentenced to four years in prison for being complicit in the murder of 300,000 Hungarian Jews in what is likely to be one of the last Nazi trials.

Oskar Gröning, 94, looked on impassively as judge Frank Kompisch delivered the verdict, calling it “justice, not revenge” and telling him while he had not been directly involved in the killings he had been an integral cog in the machine of the Auschwitz extermination apparatus.

He said Gröning had taken a “safe whitecollar job at a desk which gave you certain protection ... in a machinery designed entirely for the killing of humans” that was “inhumane and all but unbearable for the human psyche”.

While the SS had been reliant on some to carry out sadistic acts, Gröning, in his capacity as a bookkeeper – who was responsible for collecting money found in prisoners’ clothing and luggage before recording it in a ledger – had been important “precisely because of your education. Rather than being sent to the front, it was important for the war effort that you had this duty in Auschwitz,” Kompisch said.

Survivor Leon Schwarzbaum welcomes the sentencing of Oskar Göring. Guardian

Gröning’s occasional duties on the arrival ramp during the two years he spent working at Auschwitz saw him responsible for taking the luggage of new prisoners.

This role meant he had witnessed first-hand the suffering of those deported to Auschwitz, Kompisch told him: “Mr Gröning, don’t tell me you did not see the suffering, of course you saw it. You didn’t just look after the luggage to see that it wasn’t stolen .... [you] knew they were never going to see their luggage again.”

He emphasised how Gröning’s role had helped ensure the smooth running of an extremely efficient machine of death and deception, including making sure that new arrivals were not given the impression they were about to be sent to the gas chambers. This, he said, referring to evidence given during the trial by historians, would have caused panic and a potential breakdown of the system.

Gröning, he said, was typical of many who had contributed to the success of the Nazi’s final solution operation, which had been “perfectly planned so that it had many different parts with the aim of making sure that no single person can be considered responsible for everything”.

Leon Schwarzbaum, 94, who lost 30 members of his family in the Holocaust, was the only Auschwitz survivor present in court to hear the verdict. The judge made a last-minute decision on Tuesday to deliver the ruling a week ahead of schedule, which meant many of the co-plaintiffs were unable to make the journey.

Speaking of his relief, Schwarzbaum said: “I feel satisfied that justice has finally been served. Whether he goes to prison or not is not really relevant. I’m the same age as him, and seeing him in court just reminded me of being in Auschwitz as a 22-year-old and being amazed to see Nazis the same age as me shooting Jews.”

But 81-year-old Eva Mozes Kors, one of the co-plaintiffs who gave harrowing testimony in court earlier in the trial, criticised the sentence. “His value is not sitting in jail at the age of 94,” she said via email. “His value to society would be in speaking to students in person ... so that every time he lectures he relives those experiences. As it is, in jail he doesn’t have to talk about it – he can just rot away.”

The verdict makes Gröning the 6,657th person to be convicted of Nazi war crimes in Germany, out of a total of 172, 294 people who were investigated between 1945 and 2005.

He is only the 50th Auschwitz guard to have been convicted, out of 6,500 who have stood trial. Only a handful have served prison terms. Kompisch used his verdict to say: “A lot more could have been done.”

The verdict was welcomed by lawyers representing the more than 60 co-plaintiffs – either survivors of Auschwitz or relatives of those murdered there – most of whom travelled from their homes in the US, Canada and the UK.

Thomas Walther, who is responsible for 51 co-plaintiffs and who spent years working to bring the case, said his clients would be “damned happy that the court case has reached a conclusion”. He had yet to reach any of them on the phone when he spoke, but said when he did he would tell them that the judge’s detailed verdict, delivered over 90 minutes, “proved that the court listened closely to their testimony. There’s never been anything like this in a German court,” he added.

“What was important was that he stressed how integral all the contributors to the Nazi war effort had been and not just the leaders. He made it clear that Hitler, Heydrich and Himmler would have been very lonely had they not had other people helping them.”

He said it had also been important for his clients to see how Gröning himself had been emotionally affected by the three-and-a-half month long proceedings.

However, Gröning may never serve any of the sentence, which is subject to a decision by prosecutors and doctors that may take months to reach. Following the trial he was driven to his nearby home. His lawyers have a week to appeal the verdict.

Heinrich-Peter Rothmann, a lawyer for another of the co-plaintiffs, said he doubted whether Gröning would end up behind bars. “I’m sure they won’t send him,” he said. “But that is not important to my client so much as the fact that this trial has taken place at all, and that he has been handed a sentence.”

In a joint statement, the co-plaintiffs said: “SS members such as Gröning who took part in the murder of our families have created lifelong and unbearable suffering for us.

“Neither the criminal proceedings nor the words of the accused can alleviate this suffering. But it gives us satisfaction that now the perpetrators cannot evade prosecution as long as they live.”

Dr Moshe Kantor, president of the European Jewish Congress, welcomed the verdict, saying: “Although more than 70 years have passed since the liberation of the Nazi death camps, this trial reminds us that there is no statute of limitations for those responsible for Nazi horrors and of the real and present danger of intolerance and demonstrates the constant need to guard against antisemitism, racism and hate.”

On Tuesday, Gröning had made a final appeal to the court to recognise his contrition. He said he agreed with the prosecution’s argument that “no one should have taken part in Auschwitz”.

“I agree with that,” Gröning said. “I sincerely regret that I did not recognise that earlier. I’m truly sorry.”

Earlier in the case, while admitting his moral culpability, he had said “only God” could grant him forgiveness.

Kompisch, who said the case had made a deep impact on him as a judge, affecting his “view of the world”, welcomed the fact that Gröning had stood up to his responsibilities by actively participating in the case – in stark contrast to John Demjanjuk, who during his 2012 trial in Munich for aiding and abetting the deaths of thousands of Jews in Sobibor, was wheeled into court on a gurney every day, and remained silent throughout.

Kompisch said Gröning’s cooperation had helped mitigate his sentence. “We also have to take into account your venerable age and that you probably won’t outlive your sentence,” he said, acknowledging that the trial had taken its toll on his health.

At the end of the court session a tired-looking but expressionless Gröning, dressed in a burgundy sleeveless pullover, pressed his fists into the table to push himself up from his chair before rolling his walking frame to the door and exiting the room without saying a word.

The trial was the second attempt over an almost 40-year period to bring Gröning to justice.

But after judges in Munich ruled that Demjanjuk had aided and abetted mass murder simply by working at Sobibor, a change of attitude took place among the judiciary, allowing an individual’s mere presence at a concentration camp to be considered evidence enough to secure a conviction.

The way for Demjanjuk’s case was paved by the 2006 trial of Mounir el Motassadeq, who was jailed for aiding and abetting the 9/11 murders by continuing to pay the rent of the attacks’ ringleader Muhammad Atta, long after he had left for the US, to make it appear that he was still living in Hamburg.

The last Nazis: more cases could follow

Gröning’s conviction has sent an encouraging signal to lawyers attempting to bring other remaining Nazis to trial.

A court in Dortmund is due to decide any day now whether Reinhold Hanning, a 93-year-old former SS guard at Auschwitz and a member of the SS Totenkopf division , is fit enough to stand trial. Co-plaintiffs who were at Auschwitz at the same time as him and who are prepared to give testimony in court have already been gathered.

The case of Christel Maass, who was a guard at Auschwitz around the same time as Gröning and is now in her 90s, could come to court later this year. Co-plaintiffs have been tracked down by lawyers and are prepared to testify against her.

A 94-year-old farmer from the northern German state of Mecklenburg-Vorpommern, identified only as Hubert Z, who worked as a hospital orderly in the emergency medical services squadron of the SS, stands accused of aiding and abetting the murders of tens of thousands of Jews. A decision by a court in Schwerin, the state capital, is due to be made as to whether he can stand trial.

In February, state prosecutors said they had opened an investigation into 93-year-old Hilde Michnia, who served as a guard in the Bergen-Belsen and Gross-Rosen concentration camps and is suspected of forcing prisoners on an evacuation march in 1945 during which approximately 1,400 women died.