Delgado said an initial investigation shows that speed was a factor in the crash.
Officials did not immediately release the names of those involved, pending notification of their families.
The crash happened about 11:30 p.m. Wednesday at Pennsylvania Avenue and 21st Street NW in James Monroe Park, a few blocks from the Foggy Bottom Metro stop.
On Thursday morning, the park was still blocked off with police tape as Park Police cleanup crews loaded debris — including parts of the bench, branches, a bike and a cooler — into a pickup truck.
Only concrete blocks remained of the bench where the two people had been sitting.