One of the suspects, a 14-year old, was arrested over the weekend.
New York Senator Chuck Schumer is working to get quick visas for Yoo's parents to come to the U.S. from China to claim their son's body.
By all accounts, Yu was a mild-mannered graduate student who was minding his own business as he walked home one night last week near the normally safe campus in upper Manhattan.
Police say Yu was suddenly jumped and beaten before he broke away and was fatally struck by a car. It was a senseless death made more shocking by reports identifying the suspect - a skinny 14-year-old who may have assaulted the victim on a whim.
The attack "was predatory in nature," a city attorney, Keith Brown, told a judge on Monday at a family court hearing attended by the boy and family members. A police detective also testified that the suspect showed no remorse while confessing to the crime.
The boy, whose name was not released because he was a minor, appeared to fight back tears as the judge decided to lock him up in a juvenile detention facility until his next court date on Thursday.
Afterward, two women identifying themselves as the suspect's aunts said the death was an accident caused by "child's play," and insisted their nephew was indeed remorseful.
"He cries night by night," one said.
The boy's mother, who lives in Jacksonville, Fla., and suffers from depression, decided to "ship him" to New York at the beginning of the year to live with relatives because "she could not handle (him)," according to a social worker's report. The judge said she had no choice but to leave the suspect in custody, because of the seriousness of the allegations and because no one in the city had legal custody of him.
Yu, a Ph.D. candidate in statistics and a teaching fellow in the Graduate School of Arts and Sciences, was a native of China and an only child, friends said. They described him as a friendly, gifted classmate who was active in the Columbia University Chinese Students and Scholars Association.
Police originally suspected Yu was the victim of a robbery at about 9 p.m. Friday as he walked home from Sun's home in the Morningside Heights neighborhood. But two other boys who were with the suspect at the time later told investigators it was a crime of impulse, police said Monday.
"Watch what I do to this guy," the attacker said before pouncing on Yu, according to the other boys. The suspect himself insisted he had been egged on by his friends, police said.
Authorities allege Yu's assailant, who was average size for his age, grabbed and struck him him several times on the center divider on Broadway. When Yu broke free and ran across a southbound lane, he was struck by a Jeep Cherokee.
The victim was pronounced dead at a nearby hospital. The driver of the car was not charged.
Police were able to identify the suspect by studying footage from a security camera that showed the three boys fleeing the scene on foot.
On Monday, Sen. Charles Schumer said he would seek to smooth the way for Yu's parents to travel to the New York from China's Shandong Province to claim their son's body.
"These parents have already suffered such a great loss and do not deserve to now be caught in a bureaucratic morass," the New York Democrat said in statement. "Minghui Yu was part of the New York community and our thoughts and prayers are with his family and friends today."
Though the death raised questions about the safety of the neighborhood, crime statistics from the 26th Precinct encompassing Columbia indicate that in the past several years it has become relatively safe.
There were no murders in 2007, and none so far this year. Reports of robberies were up to 52 from 40, and assaults up to 21 from 20 through March 30. But police say overall serious crime in the area was down 6.1 percent, and has dropped nearly 78 percent in the last 15 years.
