Mary Rich, mother of slain Democratic National Committee staffer Seth Rich, at a news conference in Bloomingdale on Aug. 4. Seth Rich was fatally shot in the D.C. neighborhood a month ago. (Michael Robinson Chavez/The Washington Post)

The grieving parents of a Democratic National Committee staffer who was killed in what police say was an attempted robbery near his home in Bloomingdale last month made a tearful, urgent appeal Thursday for witnesses to come forward.

“We want to find out who killed our son,” said Mary Ann Rich, the mother of 27-year-old Seth Rich. Speaking to people who might know something but are remaining silent, the 59-year-old from Nebraska warned, “Next time something like this happens, it might be someone you love.”

Mary Ann and her husband, Joel I. Rich, 68, joined D.C. Police Chief Cathy L. Lanier on the spot where Seth Rich was killed July 10 at Flagler Place and W Street in Northwest Washington. Two American flags mark the spot on the corner; the couple drove by Wednesday night, but Thursday was their first time standing at the location.

D.C. police have said it appears that Rich’s attacker tried to rob him, though his wallet, credit cards and watch were not taken when he was shot in the back about 4:20 a.m. while walking home to a rowhouse he shared with roommates.

His parents worried that their son might have tried to fight off the assailant. Police said at the time of the shooting that they were searching for surveillance video but have not said whether any was located.

The residential area north of Rhode Island Avenue had been a virtual construction zone at the time, with streets closed for a project to alleviate persistent flooding in the neighborhood. Residents complained that the work cut off street lights, making the area dark and a target for criminals.

Street robberies were a problem for weeks before Rich was shot, and police had set up a task force and sent extra officers to patrol the neighborhood.

Last week, police arrested a man linked to 14 armed robberies in Northwest and Northeast Washington, and one of them occurred on Flagler Place, one block from where Rich was shot. Police also recently arrested a man in the only armed robbery that has occurred in Bloomingdale since the fatal shooting.

Lanier would not say whether either of those men could be linked to Rich’s killing. “We have more questions than answers,” Lanier said of the investigation. She said robbery as a motive remains a strong possibility, but she said it’s not definitive.

Rich grew up in Omaha but had always been attracted to politics. He interned for a U.S. senator and helped on two congressional campaigns while attending high school and Creighton University.

He moved to the District in 2011, worked for a national polling company and then the Democratic National Committee, where he helped develop a computer program to make it easier for people across the country to locate their polling places. The former Democratic National Committee chairwoman, Rep. Debbie Wasserman Schultz (Fla.), attended a vigil for Rich in his neighborhood.

The Riches said they were in Washington this week to attend a dinner to celebrate their son’s life. On Wednesday night, they dined with his co-workers, roommates and many friends, a tribute they said attracted more than 150 people.

Mary Ann Rich pleaded for anyone who saw anything in the early hours on the morning her son was killed to come forward to police. If there is an arrest, she said, “we can rest in peace, and your neighborhood can be safe.”