It seems to rule out one legal possibility - that the attacks were carried out in support of the advancing II AK.
I decided to look into overall military situation North-West of Warsaw on the 13th of September. Map presented earlier shows situation from 24th of Sep, which was quite different to that from the 13th as most of German infantry units were not there yet (like 18.ID and 19.ID).
Around 13th of Sep Battle of the Bzura
seems to be raging further West of Warsaw, with most of German units involved there.
German situation map from the 12th shows gap between area of the battle and Western approaches to Warsaw. That gap was about to be filled by forward elements of German 4th Panzer Divison, which after unsuccessful attempts to enter Warsaw from South-West on the 8th and 9th, was now moving in the North-Western direction, trying to squeeze surrounded Polish forces from the East, as shown by an small arrow on the map.
I found reports of commander of Polish 30th Infantry Regiment, Captain Bogdan Roznowski, who's unit was defending North-Western parts of Warsaw. Here are his notes:
12 IX. Enemy noticed in Babice (tanks repulsed), also in Młociny and Wawrzyszew, Wólka Węglowa (reconnaissance and screening). Major Decowski with his battalion attacks Babice and takes it after the withdrawal of enemy. Artillery fire increases on fork road Warsaw-Młociny-Wawrzyszew. My command post under strong artillery fire. Command post moved to Gdańska street, later to Słowackiego Street.
13 IX. Strong air raids.
The enemy tries to maintain Mlociny, then retreats. Enemy detected on other directions. Strong artillery shelling
and aerial bombardment. Large losses among the civilian population. Rail station Gdanski burned to the ground. Barrack near the railroad stations also burned.
14 IX. The enemy attacks Babice, Major Decowski repels attack. Further artillery and air bombardment. The presence of small enemy patrols and single tanks in the foreground.
Source: Zbigniew Moszumański "Defence of Żoliborz in 1939".
It clearly states presence of German units with some tanks North-West and West of Warsaw. That most likely was 4th Panzer Divison trying to secure the area.
Based on all these and earlier presented reports I marked some areas on the map below.
Yellow cirles - areas targeted by Luftwaffe - Northern District, Gdanska rail station, worker's barracks next to it, approximate location of some damaged residential buildings in northern suburbs of Marymont and Zoliborz.
Red circle - artillery bombardment of a fork road.
Blue circles - areas where German units were detected.
In the corner there is a scale in kilometers to show proximity of Luftwaffe bombings and German ground forces.
Let's all draw some conclusions....
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