While ridership data for Wednesday was not yet available, the Metropolitan Transportation Authority said that ridership on Tuesday, the day of the attack, was down by about 312,000 people from one week earlier, to about 3.05 million riders.

That total represents about 51 percent of prepandemic levels.

Ridership levels fluctuate based on many factors. It is unclear how much of the drop may have been attributed to the shooting and the related disruptions it caused as transit officials suspended some service to allow the police to investigate.

On many busy platforms, hurried riders said the Brooklyn shootings had already become a distant memory, or that their concerns had receded because of their need to make a living.

When Louie Dacunha, 30, was asked about the shooting, his reaction was, “Oh yeah, that happened.”

“I wasn’t even thinking about that,” Mr. Dacunha said. “I was just thinking, ‘I gotta go where I gotta go.’”

As Mr. James was taken into custody more details emerged about a life that included numerous arrests.

He was born in New York City in 1959, according to public records, and his sister, Catherine James Robinson, said that he moved frequently between cities.

Police officials said that he was arrested nine times in New York between 1992 to 1998, on a number of charges including possession of burglary tools, a criminal sex act and criminal tampering. He was arrested three times in New Jersey, the first in 1991, the most recent in 2007.