Leung, who had a doctorate in philosophy, would have been awarded a Ph.D. in economics at Penn in May.
Police said Leung's three assailants will be charged with murder.
Two of the suspected youths were apprehended two days after the assault and robbery "standing practically in the blood of the victim" in the park, as one detective put it.
The third suspect surrendered to police the following day. All three are in the Youth Study Center, charged with aggravated assault, simple assault, robbery, criminal conspiracy and weapons offenses.
Police said Leung was attacked shortly before 7 p.m. on Oct. 7, while apparently leaving the park after playing a game of touch football with some friends.
A man walking a large dog chased the attackers away. Police said members of the Friends of Clark Park and other witnesses said the three youths had been harassing other passers-by prior to the attack.
In an interview with a reporter a few days after the incident, a sister of one of the youths said her brother told police that the three were drinking beer in the park, and throwing stones and heckling passers-by.
When Leung walked by, the sister said her brother told police, one of his buddies "went behind the guy and hit him over the head with a bottle."
"He fell to the ground and (the other youth) jumped on top of him, grabbed a tree limb and started beating him" as the student screamed for help, the sister said.
She said her brother did not say why Leung was singled out for attack.
The sister, a 29-year-old mother of three, contended that her brother was not involved in the robbery and attack and, in fact, tried to stop the assault.
A police source, however, called the sister's version of the attack "half- true."
The source said a witness told police that he saw all three teens attack Leung, then run from the park with the victim's wallet - which has not been recovered.
