The attack on the Trainstation in Wroclaw/Breslau (one of three of such attacks, according to some sources) the specific target was German soldiers returning home for leave, (http://forum.ioh.pl/viewtopic.php?t=590 ... 11b490b7a7
), which would make this a valid military target.
As for the attack on the S-Bahnhof on Friederichs Strasse, the target might as well have been military personel. Since I don't know for sure, let's assume that it wasn't. One might still make the case that it was a military target, considering it's location: We're not talking about a workingclass neighbourhood, or a quiet suburban location. Friederichsstrasse was in the center of Berlin, just blocks away from the Airministry, the Propaganda ministry, Gestapo HQ and the Ministry of Agriculture. A successfull attack here, would therefore not just kill innocent "civillians", chances are that a number of the victims would include military personel and officials from institutions that were the foundation of the Nazi State, and active in planning and administering the German war effort.
At this point in the war, the Nazi war of aggression and following occupation had already killed millions of Polish citizens (whether Jewish or not), so it was a little too late to talk about the sanctity of civillian lives.
Were the Poles acting under legitimate authority?
Apparently the attacks were carried out by a special group under Armija Krajiowa. AK means The National Army, and was the biggest resistance movement in Poland durring the war. AK-personel was at various times treated by German Forces as legitimate combatants with rights under the Geneva Convention. As for "legitimate authority" depends on who you ask. AK recognized the Polish government in exile in London, while there was another government in exile sponsered by the Soviet Union.
If these actions did in fact occur, and the persons killed were German civilians, then the actions were indeed a crime
At this point in time, Germany had allready killed, or caused the death of millions of civillians. Germany had also specifically targeted civilian targets on numerous occasions (Warsaw, Rotterdam, London, the Baedaecker Blitz, etc.).
Any protection that German civillians would normally be given under the rules of war, was squandered by Germanys criminal ruling regime.
There is also no proof, nor reason to believe, that the AK attacks specifically targeted as high a number of civillian lives as possible.