A California jury on Thursday declared an undocumented Mexican not guilty of murdering Kate Steinle, who in 2015 was shot dead while walking on a pier in San Francisco.

After six days of deliberations by the jury in a case that had sparked enormous criticism of the "sanctuary cities," the Mexican Jose Ines Garcia Zarate, who had been deported five times from the US, was found not guilty of first-degree murder, second-degree murder and involuntary manslaughter.

Garcia Zarate's allegations and records of illegal immigration prompted the US President Donald Trump to bring up this case during his 2016 presidential campaign as he insisted on the need to strengthen immigration policies and reinforce border security.

The jury, comprised of six men and six women, three of them immigrants, instead found the Mexican guilty of possessing a firearm while on probation, a charge that leads to a maximum penalty of three years in prison; Garcia Zarate had already spent almost a year and a half in jail.

During the trial, the defense argued that the Mexican, a 54-year-old homeless, had found a gun under a dock bench which accidentally went off and killed Steinle, 32, who was strolling along the dock at the time with her father, arm in arm.

Steinle was shot in the back by a bullet that bounced off the cement floor, punctured her aorta and killed her.

The prosecutor Diana Garcia said Steinle's death was a result of an intentional act, and in the trial she presented witnesses who said they saw the Mexican man pointing the gun.

Alex Bastian, a spokesperson for the San Francisco District Attorney's Office, said that although it was not the verdict that many expected, the jury's decision will be respected.

The case has brought widespread attention to San Francisco's policy of "sanctuary city," which limits cooperation between local security forces and US immigration authorities.

Having been deported in 1994, 1997, 1998, 2003 and 2009, Garcia Zarate was again captured at the end of 2009 while trying to cross the border in Eagle Pass, Texas, and pleaded guilty to re-entry.

On Mar. 26, 2015, at the request of the San Francisco Sheriff's Department, the Bureau of Prisons (BOP) turned him over to the authorities of that city for an arrest warrant for drugs.

The warrant was issued 20 years prior, so the San Francisco authorities did not enforce it.

The Mexican, who at the time of the girl's death was on probation with a history of possessing marijuana, was wanted by the US Immigration and Customs Enforcement (ICE), which issued a retention order asking that he be held in custody in order for the immigration authorities to arrest him.

However, due to San Francisco's sanctuary city policies, the city authorities did not comply with ICE's request and released him on Apr. 15, 2015.

"Let me just remind them: they are themselves under investigation by a special prosecutor in Washington DC," defense lawyer Matt Gonzalez told reporters, referring to the political exploits that the president and members of the current White House administration made of the case.

San Francisco's Mayor, Ed Lee, said in a statement to KGO News that his city will remain a sanctuary city, regardless of what the Attorney General of the nation says.

According to the judge's preliminary investigation, the undocumented status of the accused and his record of illegal entry into the US were not taken into account by the jury in releasing the verdict.

The jury's decision has provoked criticism on social media, while the Steinle family has issued a statement saying they are shocked by the verdict.