Rojas returned from his Navy service with a drinking problem and had posted "crazy stuff" on social media, said a friend, Harrison Ramos, speaking to Reuters outside the apartment building where Rojas lives in New York City's Bronx borough.
The deceased was identified as Alyssa Elsman, an 18-year-old from MI.
Authorities say Richard Rojas was taken into custody Thursday after mowing down 23 people, including a teenager who died.
Two law enforcement officials say Rojas told officers he was hearing voices.
Rojas was reportedly under the influence of synthetic marijuana, known as K2, during the incident, ABC News reported, citing sources.
Officials were quick on Thursday to dismiss the possibility of a terrorist attack, describing the tragedy as an isolated incident. The auto was traveling in the wrong direction on the sidewalk for about three blocks before the crash occurred, police and witnesses said.
Police do not suspect a link to terrorism, but the bomb squad has responded as a precaution to check the vehicle.
Rojas drove his auto from the Bronx to Times Square on Thursday, where he sped into the bustling Crossroads of the World, hitting almost two dozen people on the sidewalk before steel security barriers finally stopped him, authorities said.
The New York Police Department has a station right in Times Square, at 43rd Street and Seventh Avenue, so the response to the incident was nearly instantaneous.
One official says Rojas told authorities when arrested previously that he believed he was being followed.
Rojas is to be arraigned Friday. Her 13-year-old sister was among the 22 injured.
According to the Associated Press, the suspect initially tested negative for alcohol, but other tests would be run to determine if he was high.
New York City law enforcement officials say at least one person was killed after a vehicle traveling through the popular tourist area drove into a crowd of pedestrians around lunchtime Thursday.
The high-speed 11:55 a.m. crash - which authorities initially said appeared accidental, and which is not believed related to worldwide terrorism - left an 18-year-old woman dead at the scene and another 22 injured, New York City Mayor Bill de Blasio told reporters. "That being said, we are reinforcing key locations around the city with our anti-terror units of the NYPD", he added.
Rojas' lawyer, Enrico Demarco, had no comment.
"A woman in front on the sidewalk was hit and tossed before then vehicle reached 44th st, continued plowing people down at full speed up to 45th street, where it was stopped after crashing into more people and the light post", posted Instagram user Ed G Val, who from across the street "saw the auto speeding north on the west sidewalk of southbound 7th Ave".
Navy records show Rojas enlisted in September 2011 and was based in IL and Florida, working as an electrician's mate fireman apprentice. He was most recently arrested last week in the Bronx on a charge of menacing.
Navy records show that in 2013 he spent two months at a naval brig in Charleston, South Carolina, but not indicate why. People quickly started trying to help the injured victims.
Six months ago the city completed a $55 million, almost six-year renovation of Times Square that turned roadways into pedestrian zones.