The couple was returning home from a movie when they were assaulted early Sunday morning. Four suspects, including a 15-year-old boy, were later charged with the murder of Alan Senitt.
Senitt, a Jewish activist dedicated to fighting anti-Semitism, moved to Washington last month to do volunteer work for former Virginia Gov. Mark R. Warner, a possible Democratic presidential candidate.
The woman, whom police did not identify, was not injured.
Christopher Piper, 25, of Southeast Washington, was charged with felony murder and attempted sexual assault; Jeffery Rice, 22, Olivia Miles, 26, and the 15-year-old boy also face murder charges. Police declined to identify the boy because he has been charged as a juvenile.
Three men approached the couple with a gun and a knife demanding money and valuables around 2 a.m. Sunday, investigators said. Piper grabbed the woman and began dragging her out of sight down a driveway where he tried to pull off her clothes.
Lt. Robert Glover said the attacker made a comment "in reference to his intent to commit a sexual assault."
The two other suspects grabbed Senitt, stabbed him and slashed his throat. He lay dying while the three men fled with the woman's purse.
Police said Miles drove a green Toyota, suspected to be a getaway car.
Investigators were looking for possible links to other crimes in the city. Neighbors planned community meetings to discuss one of the most viscous crimes in the affluent Washington neighborhood.
Before moving to the United States, Senitt worked for Greville Janner, a member of Britain's House of Lords from Prime Minister Tony Blair's Labor Party. He also served twice as the elected head of the Union of Jewish Students, which represents 5,000 college students in Britain and was a Labor candidate this year for a post in the northwest London neighborhood where he was raised. Though he lost the campaign, friends said Senitt was committed to a life in public service.
"He was a serious contender for mainstream political life," said Danny Stone, a friend who leads the Co-Existence Trust, a group founded by Janner to promote Muslim-Jewish relations. "He was up and coming. He would have been brilliant. I'm sure of it."
Senitt's family, including parents Jack and Karen, sister Emma and brother James, issued a statement mourning the loss and asked for privacy.
"The Jewish community as a whole has lost one of its bright young leaders, and the wider world has lost a champion of peace and goodwill," the statement said. "It will take us a lifetime to come to terms with our tragic loss."