I am not a lawyer, but my understanding is that there are some underlying legal principles that apply to this conflict:
- Enforcement of immigration laws (federal by definition) is reserved to federal law enforcement. This means that local law enforcement and police are not allowed to arrest someone for immigration offenses.
- Most local jurisdictions do not have immediate information about the immigration status of individuals in the US. For example, if I am stopped by highway patrol I can present my driver's license for identification, but I cannot prove my status as a US citizen without going home to retrieve a birth certificate or a passport. Are you able to prove that you are here legally? The point is that local jurisdictions might have someone in their custody who is in violation of immigration laws, but they have no way of knowing that. In general, they do not have either the desire or the capability of reporting such individuals to ICE (Immigration and Customs Enforcement).
- However, whenever local law enforcement arrests someone, the individual's fingerprints and the arrest information are immediately forwarded to the FBI (Federal Bureau of Investigation). That information becomes available to the federal law enforcement agencies, including ICE. ICE knows within hours about immigration violators on their Enforcement Removal List who are in custody of a local jurisdiction.
- ICE may issue a detainer notice to a local jurisdiction indicating that they want a person held for 48 hours until ICE can come to apprehend that person. The local jurisdiction cannot hold that person. Because, constitutional protections apply to everyone in the country, independent of immigration status. If ICE issues a detainer notice for an individual who has been held in jail for a local or state offense and they are about to be released, the local jurisdiction does not have the authority to hold that individual for an additional 48 hours. Not even for any time at all; they are free to go. Detainer notices issued by ICE field agents are not arrest warrants; they do not show probable cause and they are not issued by a judge.
- containing an adequate showing of probable cause
- issued by a neutral and detached magistrate
- issued on the basis of a police affidavit that does not contain known or reckless falsehoods
- particularly describing the person to be arrested
If ICE wants to capture a person who is in the custody of a local jurisdiction, they need to show probable cause to a federal judge and get a valid federal arrest warrant. Detainer notices do not have the appropriate legal authority.