Which element is required for a warrantless arrest for possession of controlled substances?

A warrantless arrest for possession of controlled substances typically hinges on the requirement that law enforcement officers observe the substance in a public place. This aligns with established legal principles regarding warrantless arrests, as officers must have probable cause to believe a crime is being committed when they make an arrest without a warrant.

When the controlled substance is in a public place, it provides immediate and clear evidence that can satisfy the probable cause requirement. The officer's direct observation of the substance allows them to ascertain that a crime is occurring or has occurred, thereby justifying the arrest without needing a warrant.

The other elements mentioned do not uniformly necessitate a warrantless arrest in the same way. For example, witnessing distribution could indicate a crime, but is more related to trafficking rather than possession alone. Public health concerns are often considered in broader regulatory contexts and are not directly tied to the validity of a warrantless arrest. Finally, the possessor’s knowledge of the substance could be relevant in establishing a defense or in determining intent, but it does not serve as a primary factor for justifying the arrest itself. Thus, the presence of the substance in a public space stands out as the critical element needed for a warrantless arrest in the context of possession.