Democratic presidential candidates are demanding answers days after the killing of Joshua Brown, a key witness in the murder trial of former Dallas police officer Amber Guyger.

“Joshua Brown’s selflessness and courage brought some justice for his neighbor Botham Jean. We grieve again learning of Joshua’s murder. I pray for his family, his community, and all those impacted by this tragedy. We demand answers,” Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.) tweeted on Sunday.

Joshua Brown’s selflessness and courage brought some justice for his neighbor Botham Jean. We grieve again learning of Joshua’s murder.



I pray for his family, his community, and all those impacted by this tragedy.



We demand answers. — Kamala Harris (@KamalaHarris) October 6, 2019

Brown was shot to death over the weekend, just days after Guyger was sentenced to 10 years in prison for the murder of Botham Jean, a black man she shot to death last year after she said she mistakenly entered his apartment thinking that is was her own.

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She was convicted of murder in the death — a crime punishable by up to 99 years in prison. She will be eligible for parole in five years.

Brown was a key witness during Guyger's trial, having been a former neighbor of Jean who said he was present in his unit across the hall on the night of his murder last year.

Sen. Cory Booker Cory Anthony BookerThe movement to reform animal agriculture has reached a tipping point Watchdog confirms State Dept. canceled award for journalist who criticized Trump 3 reasons why Biden is misreading the politics of court packing MORE (D-N.J.) called Brown’s death “horrific and deeply troubling” and said he is “sending love and prayers to Joshua Brown’s family.”

“They deserve the justice he ensured for Botham, and we all deserve answers immediately,” he tweeted.

Horrific and deeply troubling. Sending love and prayers to Joshua Brown’s family. They deserve the justice he ensured for Botham, and we all deserve answers immediately.https://t.co/O0AWIciR82 — Cory Booker (@CoryBooker) October 5, 2019

Former Housing and Urban Development Secretary Julián Castro (D) tweeted that he grieves with Brown’s family and friends, and demands “a transparent investigation the people of Dallas can trust.”

Joshua Brown bravely stood up to injustice and helped put Amber Guyger behind bars. Three days later, he was murdered by an unknown assailant.



We grieve with his family and friends, and demand a transparent investigation the people of Dallas can trust. https://t.co/fnIF0tNCMF — Julián Castro (@JulianCastro) October 6, 2019

Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.), one of the top three candidates running for the White House, also said she was “heartsick for Joshua Brown's family and friends.”

“He bravely stepped forward and testified to bring some justice for Botham Jean, and peace for his family. We need answers—and Joshua Brown and his family need justice,” she continued.

I'm heartsick for Joshua Brown's family and friends. He bravely stepped forward and testified to bring some justice for Botham Jean, and peace for his family. We need answers—and Joshua Brown and his family need justice.https://t.co/RKlcPkUalz — Elizabeth Warren (@ewarren) October 6, 2019

Billionaire philanthropist Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE also demanded answers behind the killing, while former Texas Rep. Beto O’Rourke (D) connected Brown’s death to what he called the country’s failure to failed to “end this epidemic of gun violence.”

Joshua Brown's tragic death, just days after courageously testifying against Amber Guyger in the shooting death of Botham Jean, is horrifying. I stand with his family and activists in Dallas to demand answers on how this happened #blacklivesmatter — Tom Steyer (@TomSteyer) October 6, 2019

Brown’s death on Friday prompted outcry on social media and the “#Justice4JoshuaBrown” hashtag to go viral over the weekend.

Local authorities said they discovered Brown lying on the ground outside an apartment complex with multiple gunshot wounds on Friday night. They had arrived at the complex shortly after receiving a call about the shooting.

Witnesses said they saw a white sedan fleeing the scene shortly after hearing gunshots.

According to NBC News, police have not yet found a suspect in the case and are still looking for a motive behind Brown's murder.