Kenny Diaz of Woodbridge was stabbed to death in September 2013. He was 18 years old. (Family photo)

A woman who stabbed a Woodbridge High School student to death in 2013 was sentenced Friday to 18 years and eight months in prison in a crime a prosecutor called “senseless, unnecessary and totally unjustified.”

In January, Diandra Samuels pleaded guilty to second-degree murder in the killing of Kenny Diaz, an 18-year-old football player at the Prince William County school.

Eleven others, several of them juveniles, faced lesser charges in the case. At earlier hearings, witnesses described a series of events that started with a drug deal and ended with three cars of people abducting Diaz and taking him to the woods, where Samuels, 20, attacked him.

“This was a mob action, and this mob had one leader, and that was Miss Samuels,” Prince William County Assistant Commonwealth’s Attorney Richard A. Conway said in court. He asked for a sentence of at least 30 years.

During the hearing, Samuels tearfully apologized to Diaz’s family. “I am so sorry I took your boy from you,” she said. “It eats me up, and it haunts me.”

Diandra Samuels, 20, of Woodbridge, was sentenced for the murder of Kenny Diaz. (Courtesy of Prince William County Police)

Maria Noriega, Diaz’s aunt, said she wished that Judge Richard B. Potter had chosen a harsher punishment. But she also said that her heart went out to relatives of Samuels, several of whom were sitting just a few rows behind the Diaz family in court.

“I feel sad for her family. I’m a mom,” Noriega said.

She said that Diaz, one of the kindest people she knew, always complimented her cooking. She misses making his favorite rice for him, she said.

The events that led to Diaz’s death began when he and a friend went to purchase marijuana from Samuels and she robbed Diaz’s friend, authorities have said.

Diaz and two friends then plotted a robbery to get back at Samuels, prosecutors said, and went to her Glen Arbor apartment complex on Sept. 21, 2103, with guns. But one of her neighbors stopped their plan. The other teens fled when their robbery attempt was aborted, but Diaz was left behind.

Angry over the attempted armed robbery in their building, Samuels and numerous neighbors piled into cars — including Diaz’s, which Samuels drove with Diaz unwillingly in the passenger seat. They went to look for the two would-be robbers who got away.

Without finding the other teens, the caravan stopped at Marumsco Acre Lake Park. There, witnesses said, some people in the group dragged Diaz into the woods, and Samuels stabbed him with a curved, machete-like knife.

Six other adults have pleaded guilty to abduction or other related charges in the case.

Conway said that Samuels concealed evidence, including throwing the knife off the Woodrow Wilson Bridge in the District, and that in jail, she has been disciplined 15 times for offenses including fighting and keeping contraband.

Barry Zweig, Samuels’s defense attorney, said his client’s behavior in jail is evidence of her struggles with mental illness, alcoholism and agony over being abandoned by her parents.

One of Diaz’s high school teachers provided the court with an essay Diaz wrote two days before his death on the topic “five things I am grateful for.”

“I am grateful for being alive,” he wrote. “I am grateful for the life God has given me. I couldn’t ask for a better one.”

In court, Samuels said through tears, “It pains me every day that I took that life that he was grateful for.”