After four years and eight months, the case surrounding the tragic death of Chinese student Ji Xinran came to an end on Friday when a California judge sentenced the last defendant to life imprisonment without the possibility of parole.

Alberto Ochoa, 22, the fourth and last defendant, was sentenced for his role in the 2014 brutal baseball bat attack that led to the death of Ji, then a 24-year-old electrical engineering graduate student at the University of Southern California (USC).

A downtown Los Angeles jury found Ochoa guilty of first-degree murder, second-degree robbery and other charges in December. Ochoa's attorney has already filed an appeal of his life sentence, NBC Los Angeles reported.

Ji was robbed and attacked by a group of teenagers while walking back to his apartment alone near campus after escorting a female classmate back to her dorm after a study group shortly before 1 am on July 24, 2014.

After being beaten repeatedly with a bat and wrench, Ji staggered home to his apartment, where he was found dead hours later by a roommate.

Co-defendants Alejandra Guerrero, 20, and Andrew Garcia, 23, were both sentenced to life in prison without the possibility of parole after being convicted of first-degree murder in October 2016 and August 2017, respectively.

Getaway driver Jonathan Del Carmen, 23, who pleaded guilty to second-degree murder in August 2017, was sentenced to 15 years to life in state prison.

According to Deputy District Attorney John McKinney, the prosecutor in the case, Ochoa got out of the car with a baseball bat and was a "substantial factor" in Ji's death.

Ji's parents had traveled to Los Angeles to attend court hearings in the past, but were unable to attend Friday's sentencing.

"They understand now the case is finally over; they have to move on with their life too, they have to," Rose Tsai, an attorney representing Ji's family, told reporters at the courthouse. "But these (convictions) are all making it a little bit easier for them to survive their everyday lives."

The killing of Ji, who was his parents' only child, happened two years after two Chinese graduate students were shot to death during a robbery while sitting in their car near the USC campus.

It shocked the Chinese student community in the US and prompted discussions about overseas students' safety.

In response to the attack, USC improved security measures, which included upgrading security cameras and increasing security staff on and around the campus in downtown Los Angeles.

Ainsley Carry, vice-president for student affairs at USC, said in a letter that was read out loud by Deputy DA McKinney during Friday's sentencing that he requested "the most severe sentencing" for those who took away the life of Ji.