Police are seeking 18-year-old Jasper Spires on charges of first-degree murder in connection with the death of 24-year-old American University graduate, Kevin Sutherland. (WUSA9)

(Update: Arrest made in fatal stabbing of American U. grad at D.C. Metro)

He was a Connecticut transplant thriving in his adopted city, a policy and politics wonk known to capture sun-basked monuments, cherry blossoms and the marble halls of power in Washington with his ever-present camera.

On July 4, Kevin Joseph Sutherland stepped onto the Metro to visit friends, but he never arrived at the gathering.

In an altercation police believe was the result of a robbery gone awry, Sutherland was stabbed to death aboard a train during the Saturday afternoon rush at the NoMa-Gallaudet U station on Florida Avenue NE. Friends and authorities say they believe Sutherland was randomly attacked as he made his way through the city on a national holiday.

Police late Sunday released an arrest warrant for Jasper Spires on charges of first-degree murder, but they did not elaborate on how they identified him as a suspect and did not release any additional information about him. Police were searching for him and warned people not to approach him.

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

According to D.C. police records, Spires, 18, was arrested Thursday on an unrelated charge of robbery using force and violence in Northwest Washington. A police report said that the suspect reached for a man and asked, “What do you have in your pockets?” He then grabbed the man by the neck and pushed him against a wall, the report said. He left and was arrested by police about five minutes later.

Spires was released Friday — the day before Sutherland’s slaying — when the charge was reduced to a misdemeanor, according to court records.

A relative of Spires declined to comment when reached by phone Sunday evening, and a number belonging to Spires would not accept new messages.

Saturday’s brazen daylight attack that killed Sutherland has stunned friends, who described the 24-year-old American University graduate as kind and gentle.

He was known to enjoy the sunset at a Kenny Chesney concert with a cocktail in hand, and he decorated his student government office at American University — where he advocated for lesbian, gay, bisexual and transgender rights — with posters depicting glam shots of pop star Lady Gaga.

On his Twitter profile, he led with the Latin words of the Connecticut seal, “Qui transtulit sustinet” — “He who is transplanted still sustains.” By all accounts, Sutherland lived by the motto.

In photographs and videos Sutherland posted online, he showed reverence and adoration for D.C.’s monuments and the city’s history, highlighting what he considered the nation’s treasures.

“Whether it was taking photographs of the Lincoln Memorial or U.S. Capitol or at a get-together on a trip with friends, he was so invested in documenting that beauty of life,” said Sarah McBride, an American University graduate who was close friends with Sutherland.

On Instagram, Sutherland posted photographs of the Marine Corps War Memorial with the American flag fluttering in the twilight sky. He caught streetlamps twinkling on the Potomac. He showcased the Mall from high above, the Washington Monument and Lincoln Memorial bathed in a summer haze captured from his airplane seat taking off from Reagan National Airport.

“This view always takes the breath away,” he wrote in August 2014.

Sutherland grew up in Connecticut and first came to Washington in fall 2009. He later interned for a congressman on Capitol Hill and graduated with an interdisciplinary degree in communication, government, law and economics. At the time of his death, he was working as a digital political strategist with the firm New Blue Interactive.

“Kevin was an amazing employee and friend, we will miss him always,” said Taryn Rosenkranz, the company’s chief executive. She added that her team is “heartbroken.”

Adriana Ganci attended American with Sutherland and said that he enjoyed living in a city obsessed with politics, policy and politicians.

“He was one of those wonky kids who was made to be in D.C.,” Ganci said. “We would be out to dinner or to a bar or to a baseball game, and he would always be able to say, ‘Look, there’s Senator XYZ.’ ”

McBride, who served as student government president at American during Sutherland’s term as student government secretary, described him as “the ultimate idealist” and a champion for liberal causes on campus.

“He never sought the spotlight for anything, but his contributions were immeasurable,” McBride said. “He represented the best of AU — that selfless leadership, that selfless heart.”

McBride said that Sutherland lobbied for inclusive housing for LGBT students. He also advocated for keeping tuition costs low.

In a statement Sunday, Sasha Gilthorpe, American University student government president, described Sutherland, a 2013 graduate who served two terms as secretary, as “emblematic of who we all are and who we hope to be.”

“Kevin Sutherland was truly the best of us,” she wrote. “He was in­cred­ibly kind. He was utterly and completely devoted to his friends. He used his intelligence and his talents to champion what he believed in.”

Friend Mat Marshall said that Sutherland was known to seamlessly mesh his skills with communications and politics, dashing off a pristine and pointed campaign graphic on his computer in seconds.

“He relished in the nuance of politics, and I think it challenged him and offered him something not only where he could exercise his intellect but also his creativity,” Marshall said.

Read Scott noted that Sutherland’s apartment became a center of gravity for 20-somethings whose passion was politics. Scott said that a group of friends gathered at his home to watch the 2012 vice presidential debate and kept score.

“It was just a room full of young politicos, and it was so much fun to watch it with him and crack jokes left and right,” Scott said. “He had an infectious laugh.”

Rep. Jim Himes (D-Conn.) said that Sutherland grew up in a home where politics was frequent dinner conversation.

Himes said that Sutherland joined his campaign team in high school and later interned in his office on Capitol Hill. Himes said that he came to admire Sutherland’s sharp intellect and political savvy and trusted the college student to manage his office’s social-media accounts.

“He was really shy but a really politically attuned kid,” Himes said, noting that Sutherland’s father, Doug, was deeply involved in local politics in Connecticut and held fundraisers for his campaign for Congress.

Himes said that Sutherland was at his best discussing the intricate details of policy and debated with the congressman about the president’s proposal for a new Pacific Rim trade pact. Even when they disagreed, Himes said, Sutherland never let politics interfere with his personal relationships.

“He was about as gentle a soul as they come,” Himes said.

Sutherland’s uncle, Joe Sutherland, said that his nephew was an only child whose parents’ lives centered around him.

“He’s the closest thing I’ve ever had to a son,” Joe Sutherland said. “I don’t know how I’m going to stand it.”

Joe Sutherland said that his nephew was planning to visit Philadelphia for the holiday. He said that Sutherland always traveled with his camera and that he is concerned that perhaps the quality of his equipment might have caught a robber’s eye.

“I’m afraid that might have contributed to this case,” Joe Sutherland said. “It would have been a mighty lucrative target for a robbery.”

Peter Hermann and Clarence Williams contributed to this report.