Authorities have arrested 55 suspects, including 16 police, for participating in the murders of at least 217 people located in dozens of mass graves in the northern border state of Tamaulipas, El Informador reports. Many of the victims were pulled from buses, and the perpetrators are alleged members of the Zetas criminal gang. There’s no clear motive or design behind the murders. It’s hard to say when these arrests will bump into the law of diminishing returns, i.e., provoke the obvious question: Why weren’t these arrests made earlier?