By Jennie Pasquarella and Kate Desormeau

The tragic shooting of Kate Steinle in San Francisco has focused national attention on why her accused assailant, Francisco Lopez-Sanchez, was released from the San Francisco Sheriff’s Department’s custody in April and not deported. U.S. Immigration and Customs Enforcement and others have rushed to cast blame on the sheriff’s department for Steinle’s death. But this horrible and apparently random act of violence shouldn’t be used to push a political agenda.

Did something go wrong here? Yes. But San Francisco’s policies are not to blame for this tragedy.

Although we don’t yet have all the facts, we do know that this case was unusual. Until late March, Lopez-Sanchez was in federal custody, serving a prison sentence that normally would have ended with deportation. His sentence apparently should have ended in July 2013, but for reasons we don’t yet understand, ICE did not deport him — then or at any time over the next year and 8 months, when Lopez-Sanchez inexplicably remained in federal custody. Finally, in March 2015, the federal Bureau of Prisons sent him to San Francisco based on a 20-year-old warrant for a marijuana charge — a charge that San Francisco predictably decided not to pursue because it was a low-level offense from two decades ago.

ICE now blames San Francisco for failing to notify ICE when that charge was dropped. But the sheriff says that what ICE sent was an immigration “detainer” — a form that asks for extended detention, which he could not enforce because it was not accompanied by a warrant. Under a 2013 city ordinance and a 2015 sheriff’s policy, the sheriff’s department does not imprison people based on ICE detainers alone. Rather, like many other jurisdictions around the country, the sheriff’s department requires a judicial warrant before it will imprison someone at ICE’s request. This is not a controversial position — multiple federal courts have found constitutional defects with ICE’s detainer practices. When Lopez-Sanchez’s time in local custody was done, there was no legal basis for San Francisco to hold him.

Also relevant here is a more recent 2015 sheriff’s policy, which declines to share certain information with ICE. Even ICE recognizes that localities are not required to respond to notification requests. And there are good reasons why San Francisco decided to keep its distance from ICE: The sheriff’s department depends on the trust of the whole community, including immigrants, in order to solve crimes and keep people safe. Drawing a bright line between the sheriff’s department and federal immigration authorities is critical to maintaining that trust. At any rate, if ICE had only wanted advance notice so it could reassume custody of Lopez-Sanchez when his local charge was resolved, an outdated, legally discredited ICE detainer form was the wrong tool to use.

How could the federal government have handled this differently? If ICE had presented the Sheriff’s Department with a judicial order authorizing detention, San Francisco could legally have kept Lopez-Sanchez in custody temporarily for ICE—and it would have done so, under its policies. But ICE didn’t do that.

So the question remains:  Why did ICE use a detainer form that it knew San Francisco would not enforce — indeed a form that ICE itself has announced it will no longer use? Before policymakers rush to judgment, we need answers on what actually went wrong here.

Jennie Pasquarella is staff attorney at the ACLU of Southern California and Kate Desormeau is staff attorney at the ACLU Immigrants' Rights Project. Follow ACLU_SoCal.

The following was originally published in the Los Angeles Times.

We should not shred the Constitution in the face of tragedy. In the wake of the shooting death of Kathryn Steinle in San Francisco, the Sheriff's Department is being blamed for having released the man now charged with killing her, Juan Francisco Lopez-Sanchez, from jail. Presidential candidate Hillary Rodham Clinton, among others, has said the city should have honored a federal request, known as a detainer, to keep Lopez-Sanchez in custody.

But the county sheriff had no legal authority to hold Lopez-Sanchez: To honor the detainer would have violated the 4th Amendment. An Immigration and Customs Enforcement detainer is not a warrant. It is not issued by a judge. And it is not based on a finding of probable cause. It is simply a request that a law enforcement agency detain an individual after his or her release date in order to provide ICE agents extra time to decide whether to take the individual into federal custody and then deport him.

ICE's use of detainers to imprison people without due process or probable cause — including not just those here without authorization but also green card holders and even U.S. citizens — raises obvious and serious constitutional concerns. Indeed, a series of federal court decisions issued last year held that detainer requests are non-binding and that local law enforcement agencies are liable for holding people beyond their release times solely on the basis of the detainers. In November 2014, Jeh Johnson, the secretary of the Department of Homeland Security, acknowledged "the increasing number of federal court decisions that hold that detainer-based detention by state and local law enforcement agencies violates the 4th Amendment."

As a result of these court decisions, jurisdictions across the country, including approximately 50 of California's 58 counties, will comply with immigration detainer requests only when they are accompanied by a judicial warrant or a judicial determination of probable cause — in other words, when constitutional requirements have been met.

Federal officials turned Lopez-Sanchez over to the San Francisco Sheriff's Department in March; they knew where he was and they should have known what they needed to do in order to ultimately deport him. Why did they merely issue a detainer? Why didn't they go to court to obtain a warrant?

ICE, through its spokeswoman Virginia Kice, has said that "obtaining judicial warrants is not only unnecessary, it would place an immense burden on both ICE and the federal courts."

But the federal court decisions contradict that. The Constitution isn't optional. It can't be disregarded for the sake of the government's convenience. So add these to the list of questions: How do federal officials believe their position can be squared with the 4th Amendment, and why is it that police across the country are able to routinely satisfy the warrant requirement, but ICE agents cannot?

These issues won't get their due if Lopez-Sanchez becomes the Willie Horton of immigration policy, distorting the politics of immigration reform generally and in particular the debate between federal authorities and local jurisdictions.

Horton, a murderer who was furloughed from prison and then committed assault and rape, starred in a lurid campaign ad in 1988; and his story was used to label politicians as soft on crime. In reaction, an explosion of tough-on-crime laws fueled the prison-industrial complex we're only beginning to dismantle today. Now we may witness the rise of a "soft on immigration" label, with politicians one-upping each other to show how tough they can be, illegally and unwisely entangling local police in immigration enforcement.

The most crucial question Steinle's tragic death raises is this: Why does ICE continue to ignore what law enforcement has repeatedly told us: Local policing must be decoupled from immigration enforcement. Surely, the government can establish a system that does not require choosing between honoring the Constitution and complying with detainer policies that violate the 4th Amendment.

Hector Villagra is executive director of the ACLU of Southern California. Follow ACLU_SoCal.