Darwin G. Bowman of Sterling was sentenced Friday to more than 43 years in prison for a slaying and an assault in 2009. (Loudoun County Sheriff's Office)

Cynthia Bennett planned to testify about the horrific assault that ended her husband’s life and irreparably changed her own.

But Bennett’s daughter Samantha told a Loudoun County judge that her mother was shaking and crying at the thought of reliving the nightmare, more than four years later.

So Samantha Bennett and sister Jennifer testified at Friday’s sentencing hearing for Darwin Giovany Bowman, 22, who last month pleaded guilty to first-degree­ murder in the death of William Bennett, 57, and aggravated malicious wounding in the assault on Cynthia Bennett.

Bowman, of Sterling, agreed to plead guilty weeks before he was scheduled to go on trial for capital murder in connection with the vicious March 2009 attack.

On Friday, Loudoun County Circuit Court Judge Thomas D. Horne imposed the maximum sentence allowed under the terms of the deal — more than 43 years in prison.

Horne said he agonized over the plea agreement and thought carefully about the testimony of several witnesses who spoke on Bowman’s behalf — including family members and experts in psychology and gang behavior. They spoke of numerous traumas suffered by Bowman as a child and adolescent.

But even a tragic background “doesn’t relate necessarily” to the crime, Horne said.

The random and brutal assault on the Bennetts left the Loudoun community reeling. The couple was taking a pre-dawn walk in their upscale Lansdowne neighborhood when they were attacked by three men, authorities have said.

Loudoun County sheriff’s deputies found Cynthia Bennett barely alive, lying in the dark about 50 yards from the badly beaten body of her husband, according to previous testimony. The trauma surgeon who treated Cynthia Bennett testified in 2011 that he had never seen such grievous injuries. She suffered lacerations and broken bones in her face and around her eyes, as well as a partially severed ear and a severe injury to her pelvic area that caused her to lose a massive amount of blood.

At Friday’s hearing, the Bennetts’ two daughters were the first of more than a half-dozen witnesses. Samantha Bennett cried as she told the court that her mother was forever changed, physically and psychologically.

And the absence of her father was a continual agony, she said: When she goes to weddings, “I can’t watch the father-daughter dance, because I’ll never have that,” she said. “If I have children, they’ll never have their grandfather.”

But most of the witnesses were called by the defense team, which argued that the traumas of Bowman’s early life left him vulnerable to the pressure of gang members. Though the attack on the Bennetts was not specifically gang-related, according to authorities, Bowman was a member of the 18th Street gang.

Bowman, who was conceived after his mother was raped by the man who agreed to transport her from Guatemala to the United States, was once kidnapped by his biological father and was subjected to physical abuse throughout much of his childhood, several witnesses said.

“He was a good son, and he always cared for me,” his mother, Dunia Bowman, testified. She added that her son “was acting very sad, and crying,” in the days following the attack.

Bowman is the second suspect to plead guilty. Jaime Ayala, 21, pleaded guilty to second-degree murder in February 2011 and was sentenced to life plus 40 years in August 2011. Cynthia Bennett testified at Ayala’s sentencing hearing and told the court that she was “living in a different world than I used to live in” since the attack.

Both Ayala and Bowman’s plea agreements require that they assist in the prosecution of Anthony R. Roberts, 24, of Middleburg, the third man connected to the case and the one whom authorities have identified as the primary attacker.

Roberts has not been charged in the attack but remains imprisoned on unrelated robbery charges. Loudoun Commonwealth’s Attorney Jim Plowman said he expected to charge Roberts in connection with the assault within the next few months.

In his closing statement Friday, Plowman described a series of exhibits submitted to the court — many of them graphic depictions of the crime. His voice faltered as he spoke of the Bennett family’s suffering.

“I’ve never felt so singularly helpless as a prosecutor,” Plowman said. “They can’t be made whole no matter what happens in this courtroom here today.”

Before Horne issued the sentence, Bowman addressed the court and apologized to the Bennetts and to his own family. He wept as he read his statement.

“I will forever be sorry,” he said. “I am so sorry to the whole Bennett family. I take full responsibility for everything, and I’m so sorry for everything.”