Already, issues are emerging in the Gray case that give cause for concern. Crucial to the prosecution’s case is the claim that the police had no probable cause to arrest Gray for possession of a knife with an automatic spring for opening and closing, i.e., a switchblade, as alleged in the arrest report. In fact, Mosby asserted publicly in her news conference announcing the charges that “the knife was not a switchblade.” This is a crucial issue because the prosecution’s case is much stronger if the officers had no grounds to arrest Gray in the first place. Otherwise, the defense can argue that they were only doing their job when Gray was put in the police van under restraints.

Indeed, the very first defense motion, filed Monday, claimed that the knife was illegal and sought permission to examine it. According to news reports, before the charges were brought, a Baltimore police task force report (not yet made public) found that the knife was “spring-assisted” and illegal under local law.

This doesn’t mean Mosby got it wrong or shouldn’t have brought the charges, but it does illustrate why, especially in police brutality cases, prosecutors must be thorough. Did she or her investigators interview the authors of the report to better understand why they reached that conclusion, or whether it was animated by bias in favor of the officers? Did Mosby ask an independent expert to examine the knife and give her an objective assessment? Did she even look at the knife? We don’t know but Mosby waited only about 24 hours after receiving the task force report before filing the charges.