The attack on William and Cynthia Bennett, a Lansdowne couple who were viciously assaulted while taking an early morning walk in March 2009, sent chills through their upscale Loudoun County community as residents struggled to comprehend the random brutality.

On Wednesday, a 19-year-old Loudoun man pleaded guilty to second-degree murder in the fatal beating of William Bennett, 57.

Jaime Ayala also pleaded guilty to aggravated malicious wounding in the assault on Cynthia Bennett, 55, who spent months receiving intensive treatment at a hospital.

Ayala, an admitted member of the 18th Street gang, faces a maximum sentence of life in prison on the charges when he is sentenced Aug. 24.

Under the terms of the plea agreement, the prosecution can refile first-degree murder and other charges against Ayala if he does not provide cooperation and testimony in the investigation and prosecution of two other people believed to be involved in the crime.

Loudoun County Circuit Court Chief Judge James H. Chamblin cautioned Ayala that he will serve time in prison.

He added that the sealed proffer of evidence - the document outlining the commonwealth's case against Ayala - was "more than sufficient for a conviction."

Relatives of the Bennetts, including their two adult daughters, attended the hearing. Their expressions were somber, and they showed little emotion as Ayala entered his guilty plea.

The Bennetts were retired from the Army. William Bennett had attained the rank of lieutenant colonel and worked as a CIA contractor for years. Cynthia Bennett worked as director of procurement for the architect of the Capitol. The couple were avid hikers and had been out for a walk March 22, 2009, when they were attacked on a popular roadway.

Residents of Lansdowne held vigils and walks in the days between the attack and the arrests.

Loudoun Chief Deputy Commonwealth's Attorney James P. Fisher said the family was aware of the agreement between Ayala and the prosecution and voiced no objection.

"They are fully in support of this," Fisher told Chamblin. When Chamblin asked whether the family wished to address the court, both daughters emphatically shook their heads 'No.'

Testimony at earlier hearings indicated that Ayala told police that he was the driver for two other men, Darwin G. Bowman, 20, of Annandale and Anthony R. Roberts, 22, of Middleburg.

The teenager said that when Bowman and Roberts got in the van, they told him that they had just robbed a woman and that they wanted to rob someone else, according to earlier testimony. Soon, the white van came upon the Bennetts walking alone.

In an interview with Loudoun sheriff's investigator John H. Smith, Ayala said he helped Bowman and Roberts burn the Bennetts' blood-stained clothes after the assault.

He said the pair laughed after the attack and ordered him to drive back to the crime scene so they could take the couple's shoes.

Bowman has been charged with capital murder and is scheduled to go to trial in July. Roberts has not been charged in the Bennett case but was sentenced to seven years in prison in December 2009 for burglarizing a gun store in Leesburg.

"This is just one more chapter in the pursuit of justice in a horrific case, but there is still a lot of work to be done," Fisher said after the plea.

Ayala was not charged with capital murder because he was a juvenile at the time of the attack. He pleaded guilty in October to unrelated charges of assault, robbery and gang participation for a fight in Sterling that took place several weeks before the Lansdowne attack.

At the request of Ayala's attorney, Corinne Magee, Ayala will stay in the Loudoun County Adult Detention Center for six months while he complies with the terms of the plea agreement.

Magee also said she was working with Commonwealth Attorney James Plowman to arrange for the removal of several tattoos on Ayala's body before he is moved to another facility, where she said they "may become a danger for him."

Magee said she was satisfied with the plea agreement.

The offer "was really fair," she said. "It made it very clear that all Jaime did was drive the van."

She said that Ayala had a difficult childhood and a number of learning disabilities and that she expected the principal of his former school to testify at his sentencing hearing.

"It's going to be a battle on sentencing," she said.

"I know what [the commonwealth] has in mind, and he knows what I have in mind. It's going to be tough." Staff writer Tom Jackman contributed to this report.