Police have identified the three students who were stabbed to death during a killing spree by a Hollywood director's son in California.

Cheng Yuan Hong, George Chen and Weihan Wang were found dead in an apartment owned by British-born Elliot Rodger, who went on to shoot dead three more people before killing himself.

Mr. Hong and Mr. Chen were Rodger's roommates, but police have not yet established whether Mr. Wang was a roommate or was merely visiting on the night of the attack.

Rodger tried unsuccessfully to get into a sorority building, before shooting three young women outside the premises - killing Veronika Weiss (19) and Katie Cooper (22).

He also shot dead student Christopher Martinez (20) outside a delicatessen.

Seven people were taken to hospital with gunshot wounds and injuries caused by the suspect's car. Two of them were in a serious condition.

The killer's parents reportedly tried to find him as he carried out the attacks, after he e-mailed them and several others - including former teachers - a 120-page document in which he described his contempt for all women.

The son of filmmaker Peter Rodger killed two women and four men, and wounded 13 people, including eight who he shot as he sped through Isla Vista near the campus of the University of California at Santa Barbara (UCSB) in his black BMW while exchanging fire with police.

In the e-mailed document, Rodger (22) - who had been receiving psychiatric help - said he planned to first kill his housemates, then lure others to his residence to continue the violence before slaughtering women in a sorority and continuing his spree.

He also said he feared that his guns might have been discovered when police visited him less than a month ago.

Cathleen Bloeser, whose son was a childhood friend of the shooter and was included on the e-mail chain, said "We could see that he was turning. He'd changed emotionally and he'd become very despondent and he wanted to get back at people".

She said Rodger talked to her son and another friend about sexual crimes he wanted to commit against women. She added that Rodger had asked for her son, Philip, and their mutual childhood friend to stay with him over the weekend at his apartment in Isla Vista.

"I have a feeling that they would have been right there as a part of it and shot as well" she said.

In a YouTube video posted shortly before he went on the rampage, Rodger complained of loneliness and rejection by women and outlined his plan to kill those he believed spurned him.

Rodger's father was an assistant director of 'The Hunger Games', a dystopian futuristic drama in which teenagers fight each other to the death.

A sheriff has defended his officers' investigation of Rodger, whom they spoke to only last month.

Deputies visited him in April at his apartment in the seaside town of Isla Vista to check on him after his family expressed concern about his health.

But Santa Barbara County Sheriff Bill Brown said the officers had found the suspect to be "timid" and decided there was no reason to take further action.

He told CBS News' 'Face the Nation' that Rodger, who had posted material online about killings and suicide, was able to "fly under the radar".

Psychologist Dr. Peter Langman, who has written about young killers, says that is not surprising.

Rodger, who had a long history of mental illness, carried out the assault armed with three handguns - all purchased and held legally.

"Obviously, looking back on this, it's a very tragic situation, and we certainly wish that we could turn the clock back and maybe change some things" Sheriff Brown told CBS.

"It's very apparent that he was able to convince many people for many years that he didn't have this deep, underlying obvious mental illness that also manifested itself in this terrible tragedy".

Meanwhile, it has been reported that the killer's parents desperately tried to find him as he carried out his murderous spree, after he e-mailed them his 'manifesto'.

Family friend Simon Astaire told CNN that Rodger's mother, Lichin, saw the e-mail on Friday night, just minutes before gunfire rang out in Isla Vista.

Mr. Astaire told the network that Rodger's mother had called his father Peter, a Hollywood film-maker, before alerting 911. The parents then set off for Santa Barbara from Los Angeles.

En-route, they heard news of the shooting, Mr. Astaire said.