#Poland closes #Russia consulate in Gdańsk in response to the railway sabotage
“In this regard, while this will not be our full response, I have decided to withdraw my consent for the operation of the last [Russian] consulate in Gdańsk,” Sikorski stated. He also noted that an official note would be sent to the Russian government within the next few hours.
https://united24media.com/latest-news/in-response-to-russian-rail-line-sabotage-poland-slashes-russian-consular-presence-fm-confirms-13576
In my opinion, this specific response hints that Russian diplomatic personnel and diplomatic bags - legally protected - might have been used to facilitate the attack.
You likely won't find it in English, but if you're seriously into Russian and Soviet relations I very much recommend book "Zdrada Sowietów. Pamiętniki dyplomaty sowieckiego" by G.Z. Biesiedowski published in Polish 1989, but I now see the original was published in Russian:
https://archive.org/details/B-001-004-570-ALL
Besedovski, a Soviet diplomat in Warsaw who defected to France, described in great detail the sabotage operations the Soviet Russia conducted in 1930's Poland.