From A Soul's Journey By Jeanne Avery.https://s31.postimg.org/9t7k8odsp/mengeletwins.jpg
We also have an accusation that massive documentation of crimes was destroyed.http://www.mengele.dk/new_page_2.htm
Once Mengele's assistant rounded up 14 pairs of Gypsy twins during the night. Mengele placed them on his polished marble dissection table and put them to sleep. He then proceeded to inject chloroform into their hearts, killing them instantaneously. He then began dissecting and meticulously noting each and every piece of the twins' bodies.
Unfortunately a strict veil of secrecy over the experiments enabled Mengele to do his work more effectively. The full extent of his gruesome work will never be known because the records he sent to Dr. Von Verschuer at the Kaiser Wilhelm Institute were shipped out in two truckloads and destroyed by the latter. Any remaining notes Mengele carried with him on his escape to South America and were never found.
From the book The Myth of Race: The Troubling Persistence of an Unscientific Idea By Robert Wald Sussman
"In February 1945, Von Verschuer managed to ship equipment, his library and boxes of records to his home in Solz (Muller-Hill 1998). He had other documents destroyed, including all of his correspondence with Menegle, before his instituate was taken over by the "enemy."
"Mengele’s Flee and Capture
By the time the Russians had entered Auschwitz, Mengele was long gone. He fled west and did everything he could to cover his tracks. Others tried to deny connection with him as well; Professor von Verschuer had Mengele’s documents removed from the institution and demolished any evidence of association with him. For two months, Mengele stayed with the Wehrmacht soldiers, the military of the Nazis, in Czechoslovakia and eventually made their way to what is now East Germany and was previously Saxony. The unit he was with was captured by Americans, but Mengele showed no evidence of affiliation with the SS. Because of his luck and lies, Mengele was freed 6 weeks after his detainment (Posner and Ware). Freedom was sweet, but what Mengele really wanted was his research documents. Soon after his release Mengele risked being captured again and entered a Russian zone where a nurse friend of his was holding his documents. His mission was a success and he then went to Munich to stay with a trusted friend. Mengele was smart in his concealment; he altered the release papers of a friend and went by the cover name “Fritz Hollman.” Using his alias, Mengele attained a job at the farm of Georg and Maria Fischer. Mengele’s anxiety over capture grew and by the spring of 1949 he decided to flee to Argentina (Lynott)."
From Mengele: The Complete Story by Gerald L. Posner.
As Mengele fled Gross Rosen, the man who had secured his posting to Auschwitz moved quickly to cover his ownt racks. Professor von Verschuer shipped two truckloads of documents from his research institute in Berlin, taking care to destroy all of his correspondence with the Auschwitz doctor. 
From In Our Hearts We Were Giants: The Remarkable Story of the Lillipuet Troupe A Dwarf Family's Survival of the Holocaust. By Yehuda Koren, Eilat Negev
Mengele's academic rival, Professor Hans Grebe, obtained a teaching position in the Department of Human GEnetics at the University of Marburg in 1953; in 1957 he became president of the German Association of Sports Doctors. Grebe, like von Verschuer, vigorously denied any collaboration with Mengele at Auschwitz. He also destroyed all incriminating documents. The medical records kept by von Verschuer at the Kaiser Wilhelm Institute are not available to researchers; in a bizarre irony, sixty years after the extermination, the Nazi doctors' Jewish victims have been transformed by German officials into esteemed patients whose right to privacy must be steadfastly safeguarded.
Um, somebody should tell Yehuda Koren and Eilat Negev that other authors are claiming these documents are supposed to be the ones that were shipped out in two truckloads and destroyed. Can these Jewish authors at least get together and get their theses straight in agreement?
Finally, I have this.https://s32.postimg.org/pealz47z9/mengeleconfess.jpg
What is noted here in red is heresay and can not be satisfactorily proven. I'm not even sure the son is telling the truth. Perhaps if that German souce in footnote 527 was located, along with a couple others, further insight could be gained into what Von Vouscher's son really said or did. Tödliche Wissenschaft. Die Aussonderung von Juden, Zigeunern und Geisteskranken 1933-1945 p. 129. (Murderous Science. The segregation of Jews, gypsies and the mentally ill 1933-1945)
Again, this would be another interesting line to look into to see what turns up.
I am more interested in the primary source for the claim that Von Verschuer destroyed two truckloads of documents. If it is in fact Miklos himself making that claim, then that poses problems for the credibilty of such a claim given his already outrageous other statements, and the apparent refusal of Mengele to kill the witnesses to his crimes, as Carlo pointed out.