LOS ANGELES (AP) — Four teenagers pleaded not guilty Tuesday to murder charges in the fatal beating of a Chinese graduate student at the University of Southern California.

According to prosecutors, Jonathan Del Carmen, 19, and Andrew Garcia, 18, Alberto Ochoa, 17, and Alejandra Guerrero, 16, fatally attacked USC engineering student Xinran Ji at around 1 a.m. on July 24, 2014.

They entered their pleas at a downtown Los Angeles courtroom, Los Angeles County District Attorney spokeswoman Sarah Ardalani said.

Xi, 24, was beaten with a baseball bat and a wrench as he walked to his apartment near the university campus. He made it back to his apartment, leaving a trail of blood, and a roommate discovered his body hours later.

Prosecutors have not yet decided whether to seek the death penalty against Del Carmen and Garcia, Ardalani said. The other two defendants are not eligible for the death penalty because they are under the age of 18.

Garcia and the two younger teens were also charged with robbery and assault with a deadly weapon. All four are due back in court on Sept. 12.

The fatal beating of Ji reverberated through the university community, particularly among students from China. In 2012, two USC students from China were fatally shot during an off-campus robbery also during the early morning hours.

In response to Ji’s death, USC announced last Friday enhanced security measures, including increased year-round security patrols both on- and off-campus. This fall, the university will also require international graduate students to complete safety education programs.