It is a very hard task to find in the Web lower (than 100,000) estimate.
I highlighted the keyword here - Web. The Internet's output tends to maximise estimates, not minimise them.
Firstly, there were never 20,000 foreign Jews in the Minsk ghetto, only 7000.
As for the overall numbers, here's Gerlach, Kalkulierte Morde, p.625
Die urspruengliche Einwohnerzahl des Minsker Ghettos wahrscheinlich geringer war als in Ueberlebendenberichten und der Literatur ueberwiegend angegeben.
(the original number of inhabitants of the Minsk ghetto was likely smaller than given in survivor reports and the literature)
5.1.42 the Minsk Stadtkommissar estimated only 15-18,000 Belorussian Jews along with 7000 German Jews. (Gerlach pp.625-6, citing Janetzke an Rosenberg, 5.1.42, StA Hannover 2 Js 499/61, Sonderheft 3, p.15ff)
killed until then:
10,000 Jewish men in Drosdy internment camp, summer 1941
5000 in August and September 1941 from ghetto
2000 from Drosdy internment camp, October 1941
14,000 from ghetto in November/December 1941 = 31,000
Hersh Smolar, the Minsk Ghetto, p.52, a survivor memoir, gives 80,000 as number registered in 1941. But the same source also gives an estimate from the Judenrat that 30,000 had been murdered by the end of 1941.
1942: (Gerlach, pp.690ff)
January-February - possibly 3000 Jews killed
2-3 March 1942 - 3412 killed
28 to 31 July 1942 - 10,000 killed, including 6500 Belorussian Jews and 3500 Central European Jews
= up to 13,000 Belorussian and 3500 Central European Jews
September 1942: 9472 Belorussian Jews alive according to Janetzke again, 2600 Central European Jews as well. (others died of hunger).
This suggests that Janetzke was under-estimating in January, but not by that much.
The discrepancy would be:
- 9472 alive in September
- ca 13,000 murdered in 1942
- ca 31,000 murdered in 1941 = 55,000 Jews
.... so there is a discrepancy of 25,000 between these figures and the number of 80,000.
Grossmann/Ehrenburg, Black Book, p.333, cites survivor saying 75,000 registered in 1941
In 1939 there were 70,998 Jews living in Minsk, plus refugees, would have been 90,000 - how many fled? There are few documented cases of resettlements of entire ghettos into the Minsk ghetto, such as occurred at Warsaw and Lodz.
The best estimate of escapees and survivors from the Minsk ghetto is 3-4,000. Higher number of 10,000 sometimes given, but this would mean 1 in 8 of the higher number successfully escaped, I don't believe that.
Best estimate would be 60,000 Belorussian (and western Belorussian/Polish) Jews were interned in the ghetto in 1941, of whom up to 46,000 were murdered by the summer of 1942, probably a little less (the January-February 1942 actions are eyewitnessed only, no documents). A certain number starved to death, 3-4000 escaped, some survived deportations.
One additional thing: the Minsk ghetto was used as a holding centre for e.g. Soviet POWs who were Jewish, such as Aleksandr Pechersky, who led the Sobibor revolt. So there is an unknown number on top of the 'natives', that have not been taken into account.
Some (ca 1000) of the deportees from 'Minsk' in the autumn of 1943 came from labour camps in Smolensk, Bobruisk and Mogilev.