After the death of 24-year-old American University graduate Kevin Sutherland, police arrested 18-year-old Jasper Spires on charges of first-degree murder. (WUSA9)

Authorities suspect that the man charged with fatally stabbing a passenger during a daytime robbery aboard a Metro train Saturday may have been high on synthetic drugs, according to several D.C. police officials with knowledge of the investigation.

Jasper Spires, 18, of Northwest Washington was arrested Monday morning on Georgia Avenue NW several blocks from Sherman Circle after being spotted by officers. D.C. Police Chief Cathy L. Lanier said the suspect was deemed so dangerous that she had fliers about him distributed to patrol officers across the city and ordered his description broadcast over the police radio every two hours.

Police said they are investigating Spires in connection to other crimes, including robberies, over the Independence Day weekend. He had been arrested Thursday, two days before the fatal stabbing, after he allegedly threatened and tried to rob a man outside a strip of stores in Friendship Heights but was freed while awaiting trial.

Spires is charged with first-degree murder while armed and was being held until an initial appearance in D.C. Superior Court on Tuesday. He is accused of repeatedly stabbing Kevin Joseph Sutherland, 24, of Northeast Washington shortly before 1 p.m. aboard a Red Line train as it approached the NoMa-Gallaudet station, headed toward downtown.

Sutherland, an American University graduate, was headed on a Fourth of July outing with friends. The Connecticut native worked as a digital political strategist for New Blue Interactive, and friends described him as being at home in a city that thrives off politics and policy. A police official said authorities believe the attacker was trying to steal Sutherland’s cellphone.

D.C. police have issued an arrest warrant for Jasper Spires, shown here in an undated picture, on charges of first degree murder. (Reuters)

Police said that there were other people in the car but that it was unclear how many saw the attack. Tens of thousands of visitors were in the District to celebrate the Fourth of July, and Metro trains are typically crowded throughout the day. Sutherland was pronounced dead inside the train.

“Obviously we’re glad they have him and hope they have good evidence that they have the right person,” said Joe Sutherland, the victim’s uncle.

Only a few details about Spires have emerged since his arrest. He grew up in Northwest Washington and graduated in 2014 from Wilson High School. He attended Louisburg College, a private two-year Methodist school in North Carolina, where he majored in environmental engineering, according to an online school profile. The college said he was enrolled from the summer of 2014 through this past spring.

Paul Spires, Jasper Spires’s 25-year-old half brother, said the arrest has shocked the family, which includes 12 siblings. Paul Spires, a local musician who goes by the name JusPaul, described the suspect as a caring brother who would go out of his way to spend time with his siblings. “It’s not rational,” he said of the charges.

Jasper Spires played football growing up, wanted to be a scientist and excelled in math. “This is real unexpected behavior of him,” Paul Spires said of the allegations. “It hurts to see all this take away the hard work he’s done.” He said family wants “to get him some help, whatever he needs.”

Paul Spires would not say whether he believed that his brother used synthetic drugs.

D.C. Mayor Muriel Bowser and Police Chief Cathy Lanier linked the sale of synthetic drugs to an increase in homicides in the District at a community meeting. (WUSA9)

If police determine that the killing is linked to synthetic drug use, it would be the latest incident in which use of the drugs has led to violence in the city. Lanier and other city officials have said it is a growing problem and have made targeting the drugs a priority. They said synthetic marijuana can produce effects similar to that of the hallucinogen PCP, which can cause psychotic and violent behavior.

Jasper Spires’s attorney declined to comment Monday.

Since turning 18 in September, Spires has had several run-ins with law enforcement. He was cited in May after police charged him with failing to pay a Metro fare in Silver Spring and was arrested the next month when police said he was lying on a bus bench for two hours outside the Bethesda Metro station and refused to move. Both cases are pending.

Spires was arrested Thursday night in Northwest Washington on more serious charges. A police report says he confronted a man outside shops in the 5200 block of Wisconsin Avenue NW in Friendship Heights. The victim told police that the man was waving a wine bottle and demanded, “What do you have in your pockets?” He then grabbed the man by the neck, pushed him against a wall and searched through his pockets, the report says.

He was arrested by police about five minutes later. According to a police report, he kicked two officers in the legs as they handcuffed him.

The police report indicates that officers forwarded to prosecutors charges­ of robbery by force and violence, a felony, and assault on a police officer, a misdemeanor. When Spires made his initial appearance in D.C. Superior Court on Friday, prosecutors downgraded the felony robbery charge to a misdemeanor simple assault. A judge released Spires pending a July 21 hearing and ordered him to stay away from the victim.

Lanier said she is not sure why the U.S. attorney’s office did not pursue the more serious charge. “We are going to look into that investigation and see what happened,” she said. “It seemed like a solid case.”

Joe Sutherland said the family is seeking more information about why Spires was released after his arrest Thursday.

“We’re pretty distraught that he was released for a similar, if not less deadly, crime two days earlier,” he said. “It’s particularly heartbreaking — if he had been held on the charges. . . . It led to a direct line to my nephew’s death. We are very distraught about that. This shouldn’t happen.”

William Miller, a spokesman for the U.S. attorney’s office for the District, said in a statement that prosecutors “determined that the facts were legally insufficient to sustain the charge of robbery that was presented by the police.” The police report notes that nothing was taken during the incident.

Miller said that after the murder charge was filed, prosecutors are working with police “to swiftly bring the alleged perpetrator before the court to face justice.”

T. Rees Shapiro, Michael Smith and Clarence Williams contributed to this report.