Himmler visited Białystok on 30 June 1941 and pronounced that more forces were needed in the area, because the massive chase after the fleeing Red Army left behind a security vacuum.

On 3 July an additional formation of Schutzpolizei arrived in the city from the General Government, led by SS-Hauptsturmführer Wolfgang Birkner, veteran of Einsatzgruppe IV from the Polish Campaign.

The relief unit, called Kommando Bialystok,[3] was sent in by SS-Obersturmbannführer Eberhard Schöngarth on orders from the Reich Security Main Office (RSHA), due to reports of Soviet guerrilla activity in the area with Jews being of course immediately suspected of helping them.

On 10 July 1941 Schaper's Einsatzgruppe was subdivided into dozens of smaller commandos (Einsatzkommandos) numbering from several to several scores of people whose mission was to kill Jews, alleged communists and Soviet NKVD collaborators in captured territories often far behind the advancing German front.

The prosecutors had called a key witness, the German Kreiskommissar in Łomża, who named the Gestapo paramilitary Einsatzgruppe B under SS-Obersturmführer Hermann Schaper in the course of Birkner's investigation.

[5][4] He was retried in Germany in 1976 for other crimes against Poles and Jews and was sentenced to six years in prison, however following an appeal this was overturned and his health was declared too fragile for a new trial.