Chinese cops spoil my party

I was in Beijing last month, and the night before I left invited some friends to join me for some food, beer, and conversation. Among those I asked to come was lawyer, activist, and Charter 08 signatory Teng Biao (腾彪). He didn't come, and didn't phone to say why. Later I found out why: he had been out visiting black jails (the illegal detention centers where petitioners are sometimes sent) and had been detained by the police for interrogation. It's kind of depressing to think that with a crime (unlawful detention under Art. 238 of the Criminal Law) taking place right in front of their eyes, the police would rather harass the people who are trying to stop the crime. Isn't this getting things backwards?