A Mexican immigrant was acquitted of murdering Kathryn Steinle, ending a case that President Trump used to make the case against illegal immigration. Picture: San Francisco Police Department via AP, File

San Francisco - An undocumented Mexican immigrant was acquitted Thursday of murdering a woman in California -- a dramatic conclusion to a polarising case that President Donald Trump frequently used on the campaign trail to make the case against illegal immigration.

Jose Ines Garcia Zarate -- who had been deported five times from US soil -- was charged with fatally shooting Kathryn Steinle, 32, in July 2015 in San Francisco. 

His attorneys argued that the gun went off by accident.

After several days of deliberations, jurors only found him guilty of felony possession of a weapon.

Trump was quick to denounce the verdict, and immigration authorities said they would work to see Garcia deported.

"A disgraceful verdict in the Kate Steinle case! No wonder the people of our Country are so angry with Illegal Immigration," Trump tweeted.

During the heated 2016 race for the White House, Trump regularly used the case to justify his proposed construction of a massive wall on the border with Mexico, and to rally support behind his hardline stance on immigration.

Read more: Trump moves to 'build that wall'

Speaking to CNN last year, Trump dubbed Garcia an "animal," saying: "Mexico pushes back people across the border that are criminals, that are drug dealers."

The divisive case reignited debate over cooperation between federal immigration authorities and police in state and local jurisdictions where the priority is crime prevention, not deportation.

Deportation planned

The case prompted many US lawmakers to argue in favor of imposing restrictions on access to federal funds for places such as San Francisco that are known as "sanctuary cities."

Such cities protect undocumented immigrants from deportation by refusing to assist or cooperate with federal immigration officials.

After the verdict, Attorney General Jeff Sessions -- who maintains an ultra-conservative agenda on immigration -- skewered San Francisco's sanctuary city status, saying its "decision to protect criminal aliens led to the preventable and heartbreaking death of Kate Steinle."

The US Immigration and Customs Enforcement agency also said the California city's "policy of refusing to honor ICE detainers is a blatant threat to public safety and undermines the rule of law."

"Following the conclusion of this case, ICE will work to take custody of Mr Garcia Zarate and ultimately remove him from the country," the agency's deputy director Tom Homan said in the statement.

Also read: Trump expected to order temporary ban on refugees

In an interview with the San Francisco Chronicle prior to the verdict's release, Steinle's family emphasised that they wanted simply to move out of the spotlight.

"We just want to get this over with and move on with our lives, and think about Kate on our terms. Nothing's been on our terms. It's been on everyone else's terms," said her father Jim Steinle.

"Even if this guy gets 100 years in prison, it doesn't solve anything; it doesn't help anything," he said.

But after the verdict's rendering, he told the paper his family was "saddened and shocked" after learning Garcia Zarate was convicted only of firearm possession. 

"Justice was rendered, but it was not served," he said.

Public Defender Jeff Adachi said Garcia Zarate was "extremely relieved."

"He knew what was at stake -- his life was at stake," Adachi said of his office's client. "I think he feels tremendous sympathy for Kate Steinle and her family -- we do as well -- but unfortunately these types of horrible tragic accidents happen every day."