A jury has sentenced Amber Guyger to 10 years in prison for the murder of Botham Jean, after viewing racist text messages sent by the former Dallas police officer.

Prosecutors had symbolically asked for a minimum sentence of 28 years. Jean, who was 26 when he died, would have turned 28 last Sunday.

In extraordinary scenes in the courtroom a few minutes after the sentence was handed out, the victim’s brother, Brandt, said he forgave Guyger.

“I love you just like anyone else, I’m not going to say I hope you rot and die just like my brother did, but I personally want the best for you,” he said.

“I wasn’t going to ever say this in front of my family or anyone but I don’t even want you to go to jail, I want the best for you because I know that’s exactly what Botham would want … and the best would be, give your life to Christ.”

After asking permission from Judge Tammy Kemp, Brandt Jean walked across the room to hug Guyger. Kemp also hugged her, after speaking with and embracing Jean’s family members.

After Brandt Jean’s gesture, Kemp herself went over to where Guyger sat and, opening a Bible to John 3:16, said: “This is where you start.” Then they hugged.

In a press conference, John Creuzot, the Dallas county district attorney, described the embraces as an “amazing act of healing”. He said of the sentence: “Personally I expected perhaps longer but I respect what [the jury] did … they reached what they thought was a just verdict.”

I love you just like anyone else, I’m not going to say I hope you rot and die just like my brother did Brandt Jean

Guyger was convicted on Tuesday of murdering the accountant, who was watching television on his couch and eating vanilla ice cream when she shot him on the night of 6 September 2018. Lawyers for Jean’s family described the unanimous verdict as a landmark in the national fight to hold police accountable for the killings of unarmed black people.

The trial then moved to the sentencing phase. Prosecutors showed the jury derisive text messages Guyger sent about working a Martin Luther King Day parade in 2018. Responding to a message that asked “When does this end lol,” she wrote: “When MLK is dead… oh wait…”

She also suggested that the crowd could be pushed or pepper-sprayed because she felt the parade was lengthy.

Martin Rivera, her former partner on the force and former lover, texted her in March, 2018, writing: “Damn I was at this area with 5 different black officers !!! Not racist but damn.” Guyger responded: “Not racist but just have a different way of working and it shows.” In another conversation two days before the shooting, a friend discusses a dog that “may be racist”. Guyger replies: “It’s okay… I’m the same… I hate everything and everyone but y’all.”

The 12-person jury was shown memes and quotations she saved on a social media account, such as “I wear all black to remind you not to mess with me, because I’m already dressed for your funeral”, and an image of a Minion character from the Despicable Me films with the text: “People are so ungrateful. No one ever thanks me for having the patience not to kill them.”

The jury deliberated for about an hour before returning their sentence. In marked contrast with the cheers that followed the guilty verdict on Tuesday, community activists reacted with anger outside the courtroom after the sentence, telling reporters that it was far too lenient.

I never wanted to take an innocent person’s life. And I’m so sorry Amber Guyger

The 31-year-old faced up to 99 years in prison. She claimed she was tired after a long work day and mistakenly went to the apartment directly above her own at the complex in central Dallas, then killed Jean because she thought he was a dangerous intruder.

Guyger denied she is racist. When she fired two shots from her service weapon while off-duty but in uniform, hitting Jean once in the chest, she said she was acting in self-defence because she thought her life was under immediate threat from a burglar.

“I never wanted to take an innocent person’s life. And I’m so sorry. This is not about hate. It’s about being scared that night,” she testified last week.

She was fired from the Dallas police department. Friends and members of Guyger’s family testified on Wednesday that she is a kind person who feels profoundly guilty and remorseful. Her defence team argued that the text messages and posts did not reflect her true character.

Jean’s mother testified that she has endured “the most terrible time”.

“I cannot sleep. I cannot eat,” Allison Jean said. She was dressed in red, her son’s favourite colour.

Facebook Twitter Pinterest Allison Jean, the mother of Botham Jean, speaks during a news conference. Photograph: Tony Gutierrez/AP

Echoing critics who alleged that police gave Guyger preferential treatment in the aftermath of the shooting, Allison accused law enforcement of “corruption” in the way they handled the crime scene. “That 10 years in prison is for her reflection and for her to change her life, but there is much more to be done by the city of Dallas,” she told reporters.

She also criticised the department’s training standards. “If Amber Guyger was trained not to shoot in the heart, my son would be standing here today. He was no threat to her. He had no reason to cause a threat to her because he was in his own apartment, in his sanctuary,” she said. “His privacy was violated, she intruded on him, and that was not enough – she killed him.”

Renee Hall, the Dallas police chief, told reporters: “Sworn testimony revealed things during this trial that gave me concern,” adding, “I acknowledge that there are things that we need to change.”

A close friend, Alexis Stossel, told the court Jean would text her basketball news and that he was a “natural leader” who led worship as a student at Harding University, a Christian institution in Arkansas. He landed a job with PwC in Dallas.

“People gravitated towards him. You just felt welcomed by his presence,” Stossel said. She wept as she recalled receiving a call on the morning after his death and slumping to the floor screaming “wait, wait, wait” at the news he had been fatally shot.

“I had never lost someone this close in my life and the feeling is just unexplainable,” she said. In disbelief, she “called him seven times and there was no answer”.

Bertrum Jean described a deep father-son bond and how they communicated via WhatsApp once Botham moved to the US from his native St Lucia. They talked every Sunday after Botham attended church. Now, his father said, “Sundays are not a good day for me, because I’m not hearing his voice.”

Wiping away tears, he added: “I’ll never see him again and I still want to see him.” He said his son was “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?”