BY VERONIKA BELENKAYA, JONATHAN LEMIRE and ADAM NICHOLS
DAILY NEWS STAFF WRITERS

Sunday, April 6th 2008, 4:00 AM

Smith for News

Minghui Yu. Surveillance video shows the popular Columbia grad student battling his attackers before fleeing into traffic, where he was struck and killed by oncoming traffic.

Smith for News

A makeshift memorial: friends were beside themselves after his sudden death.

A 13-year-old punk was arrested and charged with manslaughter Saturday night in connection with the heartbreaking death of a Columbia University graduate student, police said.

Surveillance video captured the teen assaulting Minghui Yu, 24, Friday night in Morningside Heights before he ran into traffic and was struck and killed by a car, police sources said.

A source said the arrested boy told cops he boasted to his 15-year-old pal before attacking Yu. "Look what I do to this one," the teen aggressor said, according to the source.

The 13-year-old was not identified because he's a minor. Cops were still searching for the second teen.

Investigators initially suspected Yu was a victim of a mugging, but began to back off that theory yesterday. "We don't believe it was robbery," a police source said. "It was some sort of altercation."

Yu was walking back to the Morningside Heights campus at 8:50 p.m. when he was set upon on Broadway near W.122nd St. "He'd just walked me home after dinner and I said goodbye to him," his sobbing girlfriend, Chao Sun, 24, told reporters. "He was so considerate, such a nice guy. I couldn't imagine him hurting anyone."

Yu, an only child from Shandong Province in China, was a movie buff and a painter who studied at the University of Science and Technology of China before moving to New York. He had been studying statistics for two years at Columbia, friends said.

His parents were making arrangements to travel to New York yesterday, Yu's friends said. He was also the chairman of the university's Chinese Students and Scholars Association.

"He was always helping new students from China," said Zhou Chang Yia, 27, Yu's roommate in a Columbia dorm on W.121st St.

The driver who hit Yu stayed at the scene and has not been charged with any wrongdoing.

anichols@nydailynews.com

With Alison Gendar, Dorian Block and Rich Schapiro