Mantello became a
textiles manufacturer in
Bucharest, where he met Salvadoran
consul Colonel
José Arturo Castellanos in the 1930s. After escaping to Switzerland from Romania, he went to work for Castellanos at the Salvadoran consulate in Geneva as First Secretary. He and Colonel Castellanos issued a large number of Salvadoran certificates which were smuggled into Nazi occupied territories and saved many Jews. In 1944 he became involved in the effort to halt the deportation of Hungarian Jews to Auschwitz. Mantello sent his friend, a diplomat from Romania,
Florian Manoliu, to Hungary, in order to find out what was happening there. Manoliu went to
Budapest, obtained reports from Hungarian Orthodox Jew
Moshe Krausz with the help of Swiss vice-Consul
Carl Lutz on 19 June 1944, and immediately returned with the reports to
Geneva. One of the reports was probably Rabbi
Chaim Michael Dov Weissmandl's abridged 5-page version of the full 33-page
Auschwitz Protocols: both the
Vrba–Wetzler report and
Rosin-
Mordowicz report. The reports described in detail the operations of the
Auschwitz-Birkenau death camp. The second report was a 6-page Hungarian release that detailed the ghettoization and deportation, town by town, of the 435,000 Hungarian Jews, updated to 19 June 1944, to
Auschwitz. Manilou met Mantello hours after he returned to Switzerland - very early June 21, 1944 - and gave him the reports. In contrast to many leaders who received these reports and failed to act on them, with much help from Swiss
Pastor Paul Vogt Mantello publicized the details within a day of receiving them. As a result of the press coverage, world leaders issued appeals and warnings to Hungary's Regent,
Miklós Horthy, and the mass transports by Hungary, which had been deporting 12,000 Jews every day since 15 May 1944, mostly ended on 9 July 1944 pursuant to Horthy's order issued on 7 July. The lull in deportations made it possible to organize significant rescue activities in Hungary, such as the
Raoul Wallenberg mission and continued protection of Jews by
Carl Lutz. Wallenberg arrived to the Swedish embassy in Budapest on 9 July, 1944. ==Recognition==