WASHINGTON - An undocumented Mexican, deported five times from US soil, allegedly killed an American woman last week. Although federal authorities had ordered him expelled, police freed him in San Francisco - a "sanctuary city" for unauthorized immigrants.
The seemingly senseless attack re-opened a fierce debate over cooperation between federal law enforcement - responsible for cracking down on illegal immigration - and the police in state and local jurisdictions where the priority is crime prevention, not deportation.
With the 2016 presidential election looming, the issue has a national political dimension, with Republicans accusing President Barack Obama of going soft on immigration after he issued executive orders shielding millions from deportation.
Since 2008 the government has implemented the Secure Communities program, a cooperation framework that urges state and local police to inform federal authorities when they apprehend undocumented foreigners, and to file detainer requests to keep them in custody while deportation is arranged.
Several cities have refused to cooperate in full, citing public safety concerns.
If an immigrant is afraid of law enforcement, local officials argue, he will be more vulnerable to abuse and less likely to contact police if he witnesses a crime.
The movement has grown quickly, with most undocumented immigrants now believed to be living in so-called "sanctuary cities," a controversial term coined during efforts to protect Central American refugees in the 1980s, said Marc Rosenblum of the Migration Policy Institute.
More than 350 jurisdictions in total offer limited or no deportation cooperation, according to the Immigration Legal Resource Center.
The list includes San Francisco, Los Angeles, Chicago, New York, Denver, New Orleans, national capital Washington and three states including California.
Critics left and right
"You're effectively putting a huge barrier for anyone to want to cooperate with the police if they're worried that reporting a crime or being a witness to a crime is going to result in them being deported," said Avideh Moussavian of the National Immigration Law Center.
In practice, San Francisco last year barred its police from detaining someone solely on the basis of immigration status, except under a court order. A federal administrative request is insufficient.
Exceptions exist for immigrants with felony convictions who pose a public safety risk.
Juan Francisco Lopez-Sanchez, the man accused of shooting Kathryn Steinle dead on July 1, had been charged in the past with illegally entering the United States. He was transferred to San Francisco in March on an outstanding warrant for marijuana-related offences.
The charges were dropped, and San Francisco's sheriff department released him in April. Three months later he allegedly shot Steinle, in circumstances that remain murky.
Federal immigration authorities had asked the sheriff to notify them before releasing Lopez-Sanchez. But in the absence of a court order, police said, the request was not honored.
In the 18 months to June 19, some 10,500 detainer requests have been declined in California alone, according to US Immigration and Customs Enforcement (ICE).
"Sanctuary" supporters deplored the shooting as a tragedy, but they say the policy should not be blamed for a singular brutal crime because it has proven beneficial to many communities.
Some Democrats think the case shows the limits, and dangers, of not cooperating with federal departments on immigration.
"I strongly believe that an undocumented individual, convicted of multiple felonies and with a detainer request from ICE, should not have been released," said Senator Dianne Feinstein, a former San Francisco mayor.
Hillary Clinton, the Democratic presidential frontrunner, said the city "made a mistake" in not deporting Lopez-Sanchez.
Republicans piled on too. White House candidate Donald Trump said the murder proved his claim made last month that many immigrants from Mexico are criminals.
Congressional Republicans are urging reforms that would cut federal aid to the rebellious jurisdictions.
"Every day... thousands of criminal aliens are released back onto our streets," warned House Judiciary Committee chairman Bob Goodlatte.
Obama in November ordered that dangerous felons be prioritized for deportation. The San Francisco killing could ultimately spur local and federal authorities to harmonize efforts.
"I suspect you may see some jurisdictions revisiting those policies and I know that the Department of Homeland Security is actively reaching out to jurisdictions like Los Angeles and Chicago to try and bring them back in," Rosenblum said.