A 98-year-old Hungarian who topped the dwindling list of surviving Nazi war crimes suspects has died in hospital while awaiting trial for allegedly sending 12,000 Jews to the death camps.

“Laszlo Csatari died on Saturday morning. He had been treated for medical issues for some time but contracted pneumonia, from which he died,” his lawyer Gabor Horvath told AFP on Monday.

Csatari was alleged to have been a senior police officer actively involved in the deportations from the Jewish ghetto in Kassa, now known as Kosice in present-day Slovakia, during World War II.

After being sentenced to death in absentia by a Czechoslovakian court in 1948 Csatari made it to Canada where he lived and worked as an art dealer before being stripped of his citizenship in the 1990s.

Csatari returned to Hungary, where he lived undisturbed for some 15 years until prosecutors began investigating his case in late 2011 on the basis of information from the Simon Wiesenthal Centre, which put him at the top of its list of surviving alleged Nazi war criminals.

Csatari was placed under house arrest in July 2012 and in June prosecutors charged him. They said that as commander of a collection and deportation camp in the Kassa ghetto Csatari was “actively involved in and assisted the deportations” in 1944.

Csatari, also known as Csatary, “regularly beat the interned Jews with his bare hands and whipped them with a dog-whip,” prosecutors said.

Csatari also allegedly refused requests to cut windows into airless train wagons each transporting around 80 men, women and children to the gas chambers of Nazi-occupied Europe, mostly at the Auschwitz camp in Poland.

The Jewish population in and around Kassa had been crammed into the ghetto following the occupation of Hungary by German troops in 1944. After the country’s dictator and former ally was deposed by Hitler.

The silver-haired Csatari denied committing war crimes in several hearings held behind closed doors, according to his lawyer.

The case was suspended on July 8 on grounds of double jeopardy, since Csatari has already been convicted of the charges presented.

Last week however a higher court ruled that proceedings could resume after the prosecutor successfully appealed the suspension.

Slovakia meanwhile had commuted the 1948 sentence to life imprisonment and authorities there issued a subpoena for him to attend a hearing last month, but Csatari failed to show up.

A court in Kosice had been due to rule on September 26 where Csatari should serve his sentence.

“We never believed that Csatary would live long enough to face justice on Earth,” Lucia Kollarova, spokeswoman for the Federation of Slovak Jewish Communities, told AFP on Monday.

In recent years, the authorities in Europe have made renewed efforts to bring to justice the small number of people still alive thought to have been involved in the Holocaust.

Most notable was Ukrainian-born former Sobibor guard John Demjanjuk, deported from the United States in 2009 and sentenced in Germany in 2011 to five years in prison for complicity in some 28,000 murders.

Demjanjuk died at a nursing home last year aged 91 while freed and awaiting an appeal.

The Demjanjuk verdict, stating that simply having worked at an extermination camp was enough to establish complicity in murder, set a legal precedent and Germany is now investigating around 50 suspected ex-Auschwitz guards.

German police in May arrested alleged former Auschwitz guard Hans Lipschis, 93, on charges of complicity in mass murder. Lipschis insists he only worked as a cook at the camp.

The Wiesenthal Centre, the Los Angeles-based organisation named after the famous Nazi-hunting Holocaust survivor who died in 2005, estimates that only around 60 potential defendants are still alive.

Last month as part of its “Operation Last Chance” it hung around 2,000 posters in German towns and cities appealing to the public for information on the last perpetrators of the Holocaust still at large.