Jasper Spires is seen in an undated picture released by the Metropolitan Police Department in Washington DC. (Handout/Reuters)

Jasper Spires boarded the Red Line Metro train at Rhode Island Avenue shortly before 1 p.m. Saturday, joining passengers from the District and elsewhere headed to various Fourth of July festivities, among them the Foo Fighters concert at RFK Stadium.

As the train rumbled toward its next stop, at NoMa-Gallaudet, a three-minute ride, D.C. police said, the 18-year-old Spires — who may have been high on synthetic drugs — tried to grab a cellphone tucked into the waistband of a recent American University graduate headed to a gathering with friends.

The two struggled, police said, and the terror began.

Police and a witness interviewed said passengers trapped in the moving train huddled at both ends of the car and watched in horror as Spires punched 24-year-old Kevin Joseph Sutherland until he fell to the floor, then stabbed him until he was dead. Court documents say the victim was cut or stabbed 30 or 40 times, in the chest, abdomen, back, side and arms. Police said the assailant then threw the victim’s cellphone and returned to stomp on Sutherland’s body.

“We were in a moving train,” said a 52-year-old woman, who spoke on the condition that she not be named because she is both a victim and a witness to a crime. “You’re not really sure what you need to do. . . . This man is holding a bloody knife. I don’t think anyone was going to try and stop him.”

Court documents have revealed that recent American University graduate Kevin Joseph Sutherland was stabbed 30-40 during an attack on a Red Line Metro train on July 4. The suspect in the attack, Jasper Spires, was arrested Monday and charged him with first-degree murder while armed. (WUSA9)

When the frenzy was over, the woman, who is from Texas and was headed to the concert with her 76-year-old father, said the attacker turned his bloody knife on them. A police report said he told her father, who lives in the District, “Give me what you got,” took $60 and threw the man’s wallet on the floor. The man’s daughter then handed over an additional $160 “to keep him from hurting her father,” a police report said. The attacker also robbed other passengers, police said.

The witness’s account and a police affidavit filed in D.C. Superior Court on Tuesday describe a harrowing incident aboard train car No. 3045 on a patriotic holiday that attracts tens of thousands of tourists to the nation’s capital for concerts, fireworks and other activities

Witnesses said and surveillance footage shows that the assailant was the first person off the downtown-bound train car when it reached the NoMa station after the killing — and that he took off his camouflage pants before jumping a turnstile. The arrest affidavit says that after clearing the fare meter, he dropped the pants and a black book bag, which a bystander picked up and held for police.

In the bag, according to the affidavit, was a washcloth with what was suspected to be blood and an AmeriHealth insurance card with Spires’s name printed on it. Police said they also found a small, black folding knife in a trash can.

D.C. police arrested Spires on Monday morning after a citywide manhunt and charged him with first-degree murder while armed. A D.C. Superior Court judge ordered him detained during an initial court appearance Tuesday. In the arrest affidavit, a police officer described past encounters with Spires, saying that “he acted as if he was under the influence and would talk to himself.”

Spires, who had attended a private college in North Carolina but was no longer enrolled, was previously arrested most recently on Thursday when police said he accosted a man on Wisconsin Avenue in Friendship Heights and later kicked two officers as they tried to handcuff him. Police had forwarded to prosecutors charges that included felony robbery, but because nothing was taken from the man, the U.S. attorney’s office said there was insufficient evidence to support the charge. Prosecutors instead charged Spires with misdemeanor assault, and he was freed from custody Friday.

Kevin Joseph Sutherland is shown in the undated photograph. (Family Photo)

The police affidavit says that on Saturday morning, Spires went to a police station in Northwest Washington and retrieved personal items that had been seized when he was arrested. One was a black book bag that police said is the same one left behind at the Metro station.

There was no guarantee that a felony charge would have resulted in Spires being detained. Until that time, his run-ins with police were minor — involving allegations of failing to pay a Metro fare and loitering. But his release angered Sutherland’s uncle and raised questions from D.C. Police Cathy L. Lanier.

Police said Spires was seen on surveillance video entering the Metro station at Rhode Island Avenue at 12:38 p.m. wearing a red bandanna, gold Ray-Ban aviator sunglasses and high-top sneakers. Aboard the train, he confronted Sutherland, police said.

“I watched [the attacker] drop-kick him in the head several times, like he wanted to kick his head off,” said the woman who was on her way to the concert with her father. “We saw the perpetrator kicking the man. He had him on the ground, punching him, kicking him and stabbing him.”

The woman said Sutherland was “moaning a lot. . . . Never in my life have I seen anything like this. I saw [the attacker] bent over him. I did see the bloody knife in his hand.”

The woman, who said she was among about 10 passengers on the car, pulled out her phone and called 911. Another passenger, she said, moved forward on the train to get help. Police said Spires robbed other people on the car, although the timing was not immediately clear. He has not been charged in those robberies.

The arrest affidavit says Spires walked through the car and asked people, “What y’all got?” and then rifled through a man’s pants, taking a fare card and a wallet. Police said he took $65 and threw the wallet and the fare card to the ground.

The 52-year-old woman said she was terrified. “I would have to say that my instinct was to stay put and try to become as small as possible,” she said. “I’m looking, but I don’t want to be noticed by him.”

During the robbery, she said, “I really thought when he had my dad stand up and he was standing up close to him that he was going to knife him. I didn’t know what he would do after he got money off my father.”

She said her father’s shirt, pants and wallet were stained with blood.

The woman said she and the other passengers told one another that it was too dangerous to intervene. “I think we were all trying to stay away from him considering he had a knife,” she said. “People who were in front of us were saying, ‘Don’t do that.’ ”

The woman told the attacker that she was not looking at his face, even though she had already gotten a good look at him.

“I did not want him to think that he had to hurt us because we would identify him. I wanted him to think that he could walk away from this, and that’s what he did.”

When the train pulled into the NoMA-Gallaudet station, the attacker left. “He did not run,” the woman said. “He walked. He walked very quickly.”

Mary Pat Flaherty and Faiz Siddiqui contributed to this report.