LOS ANGELES (Reuters) - four people, two of them juveniles, have been arrested in the robbery and beating death last week of a Chinese graduate student near his off-campus apartment, Los Angeles Police officials said on Monday. The body of Xinran Ji, 24, an electrical engineering student who enrolled at the University of Southern California in 2013, was discovered on Thursday morning at his apartment, a few blocks away from where Police said he had been attacked some six hours earlier.