Kate Steinle’s murder fueled national outrage and became a flashpoint in the divisive debate over the twin issues of illegal immigration and U.S. sanctuary cities, and now her accused killer is getting his day in court.

A homeless illegal immigrant from Mexico is charged with the slaying which became a signature issue for Donald Trump as he was running for president. Trump invoked the murder in calling for the construction of a wall on the Mexican border and stepping up deportations and cracking down on illegal immigration.

The 32-year-old woman and her father James Steinle were strolling on San Francisco's Embarcadero on July 1, 2015 when she was shot.

Her father testified Monday that before she died, she said to him: “Help me, dad.” The prosecution said those were her last words.

Two days after Steinle was shot, Trump released a tough statement on the killing.

"This senseless and totally preventable act of violence committed by an illegal immigrant is yet another example of why we must secure our border immediately," he said.

"This is an absolutely disgraceful situation, and I am the only one that can fix it. Nobody else has the guts to even talk about it. That won't happen if I become president."

Jose Ines Garcia Zarate, 54, admits shooting Steinle but says it was an accident.

A jury of six men and six women began hearing arguments Monday in the courtroom of Judge Samuel Feng.

“This is the gun fired at a young woman named Kathryn Steinle on pier 14,” prosecutor Diana Garcia told the jury in her opening statement.

She pointed to Zarate, and said, “She’s dead because this man pointed a gun in her direction and pulled the trigger.”

Garcia said the prosecution’s evidence includes surveillance video from a fire station that shows Steinle falling to the ground and a splash from when Zarate threw the gun in the water.

She concluded by telling the jury when they see the video, hear the defendant’s words, hear from witnesses and hear more about the gun, they will conclude that Zarate knew what he was doing and that “he meant to shoot people on pier 14 and ended up killing Kate Steinle.”

Defense attorney Matt Gonzalez said during his opening statement that his client hadn't stolen the gun, but rather found it on the pier, and it went off as he unwrapped the T-shirt.

He showed the jury surveillance video, attempting to prove that someone else could have left the gun where Zarate was sitting and argued that Zarate threw the gun in the water to make it stop firing.

Gonzalez portrayed Zarate as a homeless man who didn't speak English well and didn't really understand what was going on. The attorney showed video from Zarate's initial police interview in which he repeatedly said he didn't know why he shot Steinle and why he was aiming in that area.

But the prosecution said when Zarate was interviewed by detectives he first said the gun went off when he stepped on it, and then said it was wrapped up in a bag and that it somehow went off. Garcia said that eventually he admitted to deliberately firing the gun, but without explaining why, except at some point to say he was aiming at a seal.

The defense attorney told the jury that there has "never been a ricochet charge as a murder in San Francisco" and that an expert "couldn't make this shot if he tried."

Gonzalez concluded by saying, "If this had happened to a college kid or a Swedish tourist - if they had accidentally fired a gun - would they be charged with murder?"

The jury also heard from Jim Steinle, who was with his daughter on the pier when she was shot.

In a brief but emotional testimony, Jim described his close relationship with his daughter and their love of taking selfies together, one of which was taken moments before the shooting.

He cried on the stand as he recounted the details of his daughter's death. Jim said after she was shot and fell to the ground, "she looked at me with her arms out and said, 'help me dad' ...and I grabbed her and held her."

Zarate had a criminal record and had been deported several times at the time of the shooting.

Just before the shooting, he had been transferred to the San Francisco County Jail after serving a prison sentence for illegal reentry.

He was being held on a 20-year-old marijuana charge that prosecutors dismissed.

The San Francisco sheriff then released Zarate from jail despite a federal immigration request to detain him for at least two more days for deportation. The sheriff's department said it was following the city's sanctuary policy of limited cooperation with federal immigration authorities.

San Francisco, as a sanctuary city, honors immigration holds only if the person has a violent record or if a judge vetted the hold or approved a warrant.

At the time of the Steinle shooting, Trump was trailing most of the field running for the GOP presidential nomination.

Two weeks later after issuing his statement he was in first place.

As president, Trump has threatened to withhold federal funding to so-called sanctuary cities such as San Francisco. The threat has been met with lawsuits to stop the president from moving forward.

The gun Zarate fired had been stolen from the car of a Bureau of Land Management ranger several days before the shooting.

The trial is expected to last four to six weeks.

Fox News' Jennifer Girdon in San Francisco and The Associated Press contributed to this report.