The group that did this posted an article on their website (the full video is there BTW) that explains that the BLM monument was put up in 2003 for an illegal immigrant who died from a heart attack while being deported. It was put up illegally, but the city made it official instead of taking it down.

I found an article about the event that says 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."

There's actually a Wikipedia article about it. The guy was from Nigeria and crossed the border from Germany, so IDK why they were sending him to Bulgaria.

One of the source articles goes into more depth about Omofuma himself. He was part of some group called the Ogboni, which is banned by the government of Nigeria.

The Ogboni sentenced him to death for breaking a federal law, so he fled to Germany — although it doesn't say what law he broke. Omofuma claimed it was religious persecution, but I couldn't find any more information.