A man is under arrest after he stole a car in Boston’s South End and kidnapped the female driver this afternoon. Careening briefly down city streets, he crashed the car into a van and was captured after a foot chase, Boston police said.

The victim, a 29-year-old medical student, was getting out of a car on Waltham Street to visit her boyfriend when the man grabbed her by the hair and threw her back in the car at about 3:20 p.m., said Police Superintendent Randall Halstead.

The carjacker drove off, but crashed into the van a couple of blocks away on West Dedham Street. A civilian witness saw the crash and alerted utility workers who, in turn, informed a detail officer, Halstead said.

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That officer chased the suspect and captured him near O’Day Playground, Halstead said. “I just want to thank that civilian who stepped up,” Halstead said.

“This is a classic example of ‘See something. Say something.’ ... This is the basic building block of community policing,” he said.

Police identified the suspect as Joel Cartagena, 36, of Woburn. He is to be arraigned Friday on charges of kidnapping, carjacking, and assault and battery causing injuries.

Asked if Cartagena intended to sexually assault or rob the woman during the alleged kidnapping, Halstead said he had not yet spoken about a motive with detectives, but it appeared to be “a crime of opportunity.”

The woman was taken to Boston Medical Center for treatment for minor injuries.

Idalia Flores, 44, of Hyde Park, said she was inside Vejigantes restaurant on West Dedham Street across the street from the Villa Victoria housing development when the car crashed into the van.

She said she saw the man flee, and spoke to the woman, who had a bloody nose and bruises on her face, and said the assailant had tried to steal her car.

“She said he pushed her into the passenger side, but pushed her head down [and grabbed] her hair,” Flores said. “It was a scary moment for a moment there.”

Junior Gonzalez, 40, of Mansfield, said he was in the neighborhood visiting his mother when the crash occurred.

Gonzalez said he chased the suspect and caught up with him on a nearby street. The man did not struggle and said, “I didn’t do it,” according to Gonzales.

“He said she wanted to buy some drugs, and he was taking her to the spot,” Gonzalez said, adding that police soon arrived and took the man into custody after questioning him.

Gonzalez said he gave chase because he knew the woman had been harmed.

“That could be somebody’s mom, somebody’s sister,” Gonzalez said. “I’m just happy he got caught.”