The two men, strangers to each other, were waiting at the Rhode Island Metro station as a train pulled up the afternoon of July 4, 2015.

Jasper Spires, then 19, had just dropped out of his first year in college. Kevin Sutherland, 24, an American University graduate on his way to meet friends, brushed past him to step into the train's car.

Spires, who carried a knife, followed Sutherland onto the train. With one hand, he grabbed Sutherland's cellphone. With the other, he began stabbing and cutting. Within moments, Sutherland was dying on the floor as other horrified passengers watched. Spires kicked Sutherland before trying to rob another passenger and then running off.

A D.C. prosecutor recounted the details of the attack in court Thursday as Spires pleaded guilty to first-degree murder while armed.

Sutherland's parents said the plea brought them some relief but no answers for why Spires attacked, inflicting nearly 30 wounds.

"He ended our son's life and ended his own life, too, and we just don't know why. What happened?" Sutherland's father Douglas said outside D.C. Superior Court. Sutherland added that Spires seemed like "a bright kid."

His wife Theresa interjected. "But he still has his life," she said. "Kevin does not."

The Sutherlands agreed that if Spires had gotten to know their son, the two might have found things in common and even become friends.

"Everyone loved Kevin. He just had that type of personality where everyone just loved him," Douglas Sutherland said.

[Horrified passengers witness brutal slaying on Metro car]

The plea came after more than two years of court hearings and mental evaluations. It was an emotional hearing as about 40 or so of Sutherland's college friends joined Theresa and Douglas Sutherland in court. They wore Sutherland's photo on buttons on their lapels. Some wiped away tears.

Prosecutors and defense attorneys have considered whether robbery was the motive or if drug use or mental illness contributed to the attack, but they never arrived at a clear answer. Spires threw Sutherland's cellphone down after the stabbing and did not take anything else from the dying man. Spires was suspected of being high on synthetic drugs, but there was no evidence of drugs in his blood when he was arrested two days later. Psychiatrists at St. Elizabeths Hospital, who repeatedly examined Spires after his arrest, determined that although Spires did suffer from a mental illness, it was not so severe that it would have led to such a violent attack.

As part of the plea agreement, District prosecutors and Spires's public defenders agreed to a prison sentence of between 30 to 35 years. If Spires had gone to trial and been convicted, he would have faced a maximum sentence of life without parole. Spires is scheduled to be sentenced Jan. 12.

Kevin Sutherland, like others on the train, was headed to meet friends for a Fourth of July outing that day. Three months before his death, Sutherland had started working for a Web-based political fundraising group that linked members of Congress with their constituents. The Connecticut native was an only child.

Spires, who had been living in and out of his parents' Northwest Washington home, had attended Louisburg College, a private two-year Methodist school in North Carolina. He left in 2015, but it was not clear why.

[Man arrested in fatal Metro stabbing]

Spires was arrested two days after the killing and was charged with first-degree murder. Since then, he has been in custody between D.C. jail and St. Elizabeths, the District's psychiatric facility. At one of Spires's early court hearings, he smiled, interrupted the judge and seemed confused about why he had been arrested. A judge suggested that a mental evaluation would be appropriate.

Spires has undergone numerous psychiatric evaluations by doctors at St. Elizabeths, who determined that he suffered from a mental illness.

At one point, Spires's attorney alerted the judge that they planned to argue their client was not guilty by reason of insanity, but they ultimately did not pursue that defense.

In May, psychiatrists concluded that Spires's illness was not so severe that it should have prevented him from conforming his behavior. They also determined Spires was competent to assist in his own defense.

After the hearing, Spires's attorneys and family declined to comment.

At the Thursday hearing, Spires appeared well-spoken, coherent and conversational as Judge Judith Bartnoff questioned him to determine if he understood what he was pleading to and his legal options.

"How are you, Mr. Spires?" Bartnoff asked. "Good. How are you?" Spires responded. Then Bartnoff asked if he was on any medication and, if so, did the medication help him think more clearly. Spires laughed and said, "Yes."

Spires, standing next to his attorneys, then explained to the judge that if he had pursued an insanity defense, prosecutors would have had to prove that he killed Sutherland, and then there would be hearings about Spires's mental illness.

Bartnoff seemed impressed with his understanding. "You really do understand this," she said. Spires smiled.

"This is a very difficult and unfortunate circumstance, but I appreciate that Mr. Spires knows what he is facing and he is taking responsibility for it and we won't have a trial," Bartnoff said.

After the hearing, Spires's attorneys and family declined to comment.

Spires will remain at St. Elizabeths until his sentencing.