At the end of the video: it shows their website address, which is patrioten-in-bewegung.info. It took forever to load, but eventually let me in. Apparently the group is called Patrioten In Bewegung, which is German for "Patriots on the Move."

Here's their article about this event in particular. It has the full video, which begins with an introduction in German about the BLM monument and the victims they're honoring with the WLM monument.

I Google translated the page (my German sucks) and it says the BLM monument was built for an illegal immigrant who died from a heart attack while being deported. The monument was put there illegally in 2003, but the city of Vienna made it an official monument instead of taking it down.

They have a copy of the video on BitChute which loads faster.

An article about the event says the illegal immigrant was being deported to Bulgaria in 1999 and

"Due to strong resistance from his side, the police officers who escorted him handcuffed and gagged him, and he suffocated."