Gunman lived with first three victims.
Rodger, 22, carried out a deadly gun and knife rampage near Santa Barbara, California, after emailing a chilling manifesto outlining his intentions to his parents and therapist.
The first three victims killed in the spree on Friday night were stabbed in Rodger's own apartment.
They were University of California Santa Barbara students Cheng Yuan Hong, 20, George Chen, 19, and Weihan Wang, 20, the Santa Barbara sheriff's department said.
A statement from the department said: "They were found deceased with multiple stab wounds in Rodger's apartment located in the 6500 block of Seville Road in Isla Vista.
"Hong and Chen are listed on the lease for the apartment as tenants, along with Rodger.
"Sheriff 's investigators are in the process of determining whether Wang was also a room-mate or was visiting the residence."
The statement added: "Sheriff 's investigators believe Rodger killed these victims prior to going on a shooting rampage in Isla Vista around 9.27pm on May 23.
In all, six innocent people were killed and 13 others were wounded. Rodger died in the incident, possibly from a self-inflicted gunshot wound."
Katherine Cooper, 22, and Veronika Weiss, 19, were shot outside the nearby Alpha Phi sorority house.
The sixth victim, Christopher Michael-Martinez, 20, was shot at a delicatessen.