At a press conference, Executive Assistant Chief of Police Ashan M. Benedict said the incident began as an altercation onboard a Metrobus near 14th Street and Potomac shortly after 9 a.m.
Benedict said a person with a gun was engaging random passengers on the bus and followed one of them off before opening fire and shooting them in the leg.
The gunman then entered the Potomac Avenue Metro station and took the escalator to the station platform where they approached a person who was trying to buy a Metro card. Benedict said the gunman shot that person and attempted to drag them over the faregate turnstile before the victim was able to break free.
The gunman — who police identified as 31-year-old Isaiah Trotman of Southeast D.C. — then went further down the escalator and confronted a woman who was believed to be a customer. Benedict said a Metro transit employee who saw what was going on attempted to intervene and was shot and killed by the gunman.
A second Metro transit employee then approached the shooter - who entered and exited the train that was stopped at the platform - before being taken into custody by officers.
Metro CEO and general manager Randy Clarke called it "an incredibly sad day."
In a statement later on Wednesday, Metro identified the employee who was killed as Robert Cunningham, 64, a longtime mechanic in Metro's power department. The statement called Cunningham a "heroic employee," adding that Metro has lowered its flags to half-staff in his honor.
Clarke released the following statement after Cunningham was identified:
"Today, I feel profound sadness about the loss of our Metro family member, Robert Cunningham. We grieve for our employee, his family, and all who have been affected by this senseless tragedy. I appreciate the outpouring of support Metro has received today. Gun violence must stop. Unfortunately, Metro is not immune to the violence that our country is experiencing right now. These senseless acts must be addressed together by our leaders and community. We will take time to process this loss and take care of our employees. We are all hurting and will continue to lean on each other for support."
Metro Board Chair Paul C. Smedberg also released the following statement:
"On behalf of the Metro Board, words cannot express how saddened we are to learn about the death of Mr. Cunningham. We understand that the employee acted with extreme bravery to help a customer who was being threatened by the shooter. To the family of the Metro employee, please accept our sincerest condolences. The Board is working with management to support the Metro family."
"I just want to send my deep condolences to the Metro family," said D.C. Mayor Muriel Bowser at the scene Wednesday. "We don’t know a lot about this shooter at this moment – other than we had a person with a gun who has created yet another tragedy in our city. We will work hand-in-hand with Metro to complete this investigation as we move forward."
On Thursday, Metro officials shared a picture of their tribute to Cunningham.
The transit system also shared out a GoFundMe page that has been set up to help Cunningham's family with expenses.
Wednesday's shooting is the latest in a series of violent incidents that have plagued the transit system in recent months.
In December of last year, a woman and two teens were shot at the Benning Road Metro station after a juvenile gunman opened fire during a fight.
Also in December, an off-duty FBI special agent shot and killed a person inside Metro Center station.
Just days into the New Year, a 17-year-old was killed and a 14-year-old was wounded during a shooting at a southeast D.C. Metro station.
Several weeks ago, two children and a man were shot after an altercation that started on a Metrobus in the Brightwood neighborhood of Northwest D.C.