He killed 11 people before he was shot and wounded and surrendered to police. Mr Bowers was charged with 63 federal counts, including 11 counts each of obstruction of free exercise of religion resulting in death as well as hate crimes resulting in death. He was convicted on 16 June on all counts.
Nearly five years after the shooting, Bowers has now been sentenced for his role in the shooting. A jury sentenced him to die by federal execution on 2 August 2023.
In the months leading up to the shooting, Mr Bowers was spewing bigoted and antisemitic vitriol online, investigators say.
He called immigrants "invaders" and posted racist memes, including some that accused Jewish people of being the "enemy of white people."
On the day of the shooting, he posted a message to a web forum, saying "I can't stand by and watch my people get slaughtered. Screw your optics, I'm going in."
He then proceeded to murder 11 people at the synagogue.
After his arrest, police learned that Mr Bowers had 21 weapons registered to his name. He was otherwise unknown to law enforcement.
They then began to review Mr Bowers' online presence, finding an account on Gab — a supposedly free speech oriented, right wing social media alternative to the likes of Twitter — where he posted a steady slew of hate. His bio included the phrase "Jews are the children of Satan" and his posts consisted of anti-Jewish slurs and conspiracy theories, according to the New York Times.
The conspiracy theories included allegations that Jewish people were smuggling Muslims into the US, and another showing an image of the Auschwitz concentration camp, with the photo doctored to make its infamous gate read "Lies Make Money."
Days before the shooting he called then-president Donald Trump a "globalist" — often a term carrying antisemitic implications — and said "there is no #MAGA as long as there is a k*** infestation."
The omitted word is a racial slur used against Jewish people.
Police claim that after being shot and wounded at the synagogue, Mr Bowers said: “These people are committing genocide on my people. I just want to kill Jews.”
His defence attempted to have that quotation barred from consideration at his trial, arguing he made the statement before he was read his Miranda warning. A judge denied the motion.
The alleged gunman worked as a trucker before the shooting.
Prosecutors argued that hate drove Mr Bowers' alleged attack on the synagogue.
“The depths of the defendant’s malice and hate can only be proven in the broken bodies” of those killed, and through “his hateful words,” Assistant US Attorney Soo C Song said during her opening statement.
Prosecutors claimed in an earlier filing that Mr Bowers “harbored deep, murderous animosity towards all Jewish people.”
The defence — after unsuccessfully arguing against the use of Mr Bowers' statements to police and for a change of venue — filed a notice of mental infirmity again his potential sentencing, according to court records. They claim Mr Bowers has been diagnosed with schizophrenia and epilepsy.
His attorneys also offered a plea deal in exchange for the removal of the death penalty, but prosecutors rejected the deal.
In July, a jury found Bowers was eligible to receive the death penalty, agreeing that he met the three criteria — over the age of 18, an intent to kill, and at least one aggravating factor — for execution.
During his sentencing hearing, Bowers’ defence team asked the jury to consider his turbulent childhood and mental illnesses as mitigating factors.
“We can’t rewind the clock and make it such that this senseless crime never happened,” defence attorney Judy Clark argued. “All we can really do is make the right decision going forward. And we are asking you to make the right decision, and that is life.”
The prosecution’s expert witness regarding Bowers’ mental health said he was not suffering from delusions that might mitigate his intent to kill on the day of the shooting.
Forensic psychiatrist Dr Park Dietz — who testified as an expert witness for the prosecution in the trials of John Hinkley Jr, who attempted to assassinate Ronald Regan, and serial killer Jeffrey Dahmer — also testified for the prosecution regarding Bowers. He said Bowers suffered no delusions that would have called into question his intent to kill the worshippers at the synagogue.
Jurors ultimately decided that Bowers should be executed. They spent 10 hours over two days deliberating his sentence. The death penalty requires all 12 jurors to agree before it can be rendered.
Bowers will be the first person ordered to die in a federal execution under the presidency of Joe Biden.
The court will reconvene on 4 August at 9am to formally hand down the sentencing.