Editor's note: Amber Guyger was sentenced late Wednesday to 10 years in prison for the murder of her unarmed neighbor. Read the latest here.

The judge in the trial of a Dallas police officer convicted of murder for killing her unarmed black neighbor in his home says the jury will get instruction on a legal defense that could reduce the officer's sentencing range. The jury convicted Amber Guyger of murder Tuesday in the September 2018 killing of Botham Jean.

In Texas, the penalty for first-degree murder could be anywhere from five years to 99 years in prison. But Judge Tammy Kemp said Wednesday that jurors will receive written guidance on the law regarding a so-called "sudden passion defense."

Fired Dallas police Officer Amber Guyger becomes emotional on the stand as the defense begins their case in her murder trial Friday, September 27, 2019. Tom Fox/The Dallas Morning News/Pool

According to the Texas Penal Code, if a defendant convicted of first-degree murder can prove in the punishment phase they caused the death under the " immediate influence of sudden passion arising from an adequate cause," the offense would be reduced to a second-degree felony. If the jury accepts that Guyger's actions were taken in the heat of the moment, it could reduce the sentencing range to two to 20 years in prison.

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Guyger says she shot Jean after mistaking his apartment for her own, which was directly below. She was fired after the shooting.

This Sept. 21, 2017, photo provided by Harding University in Search, Ark., shows Botham Jean in Dallas. Jeff Montgomery/Harding University via AP

The jury heard heart-wrenching testimony from Jean's friends and family on Wednesday in the trial's punishment phase, after which they were expected to weigh Guyger's sentence. Jean's close friend Alexis Stossel recounted her last text exchanges with Jean on the night he was killed, and receiving a phone call the next morning that he had been killed.

"I hung up the phone and I called Botham seven times, and there was no answer," Stossel said.

Stossel said she wished she had told Jean the last day they spoke that she was thankful for him, saying that might have lessened her pain.

WATCH LIVE: "My Sundays have been destroyed. That's when we would speak after his worship." Botham Jean's father, Bertram, is on the stand as the sentencing phase continues. https://t.co/sBENdoDJiN pic.twitter.com/S9mDf2jMUJ — CBSDFW (@CBSDFW) October 2, 2019

Jean's father Bertrum Jean also took the stand and broke down as he testified.

How could we have lost Botham, such a sweet boy? He tried his best to live a good, honest life. He loved God. He loved everyone. How could this happen to him?" Jean said, crying. "In hindsight -- what could we have done? My family is broken-hearted. How could it be possible? We'll never see him again. And I want to see him, I still want to see him."

The defense had begun calling Guyger's friends and family to the stand Wednesday as the hearing continued.

Later Wednesday, the defense called friends and family of Guyger to testify in hopes of swaying the jury in favor of a lighter sentence.

Guyger's sister Alana Guyger, 37, testified that Amber Guyger was "the little sister I always looked up to. I always admired her for being brave. She was outgoing, she just has this positive energy that everyone gravitates towards." She described her as "kind and loving."

She said Amber Guyger has worked 40 hours or more a week since she was 16 and put herself through school. She said her sister was elated when she got a job with the Dallas Police Department.

Amber Guyger’s sister is testifying for the defense in the punishment phase of the former officer’s murder trial. She’s describing her as “kind and loving” in effort to get jury to impose a light sentence pic.twitter.com/PUaMUJZxlP — J.D. Miles (@jdmiles11) October 2, 2019

"She was so happy she was going to have a career where she could help others in need," Alana Guyger said.

Alana Guyger testified her sister was genuinely remorseful about Jean's death.

"She's expressed to me that she feels bad being with her friends and family because he can't be with his," Alana Guyger said.

Earlier Wednesday, Amber Guyger's mother took the stand and gave tearful testimony, saying her daughter had been molested by a man the mother briefly dated when the girl was 6.

Alana Guyger said her sister received counseling afterward.

"She held a lot in, and she would only talk to me about what happened," Guyger said. "I think the counseling helped bring out the feelings. She doesn't like to upset those around her."

Former police colleagues also spoke in support of Guyger.

Officer Cathy Odhiambo, who is black, described Guyger as a longtime friend, saying they met when they were servers at a TGI Friday's restaurant, and that they both eventually attended the police academy and became Dallas police officers.

"Everybody that knows her knows that Amber is the sweetest person," said Odhiambo, who added that Guyger had wanted to be a police officer for as long as she'd known her.

Odhiambo wasn't asked about text messages introduced as evidence earlier in the sentencing phase that indicated a lack of sensitivity by Guyger toward black people. However, another fellow officer, Thomas MacPherson, said that some of those texts sounded "out of character" for Guyger.

Prosecutors have given no indication in court of the sentence they will seek. Attorneys are under a gag order.