The grandmother of a student who went on a killing spree in America has spoken of her “very sick” grandson.

Elliot Rodger, 22, killed six people in a gun massacre after posting a YouTube video bragging about retribution and revenge.

Early today, it emerged three male victims were also found stabbed to death in Rodger's flat by detectives who found a "manifesto" outlining the gunman's murderous plan in chilling detail.

Lois Rodger said: “My grandson was a very sick boy. I am still very upset about all this.”

The 89-year-old, known as Jinx, of Water Lane, Smarden, near Ashford, last saw her grandson in November when she visited the family in California.

A former journalist, she said: “This is very sad for the whole family.”

Her son, Hollywood assistant director Peter Rodger, worked on the blockbuster films The Hunger Games.

He studied at Maidstone College of Art and moved to America when Elliot was a child.

Mrs Rodger’s late husband, George, was a war-time photographer and the couple lived in Smarden for more than 40 years.

She said: “If my husband was still alive he would be in terrible shock.”

The 22-year-old went on the drive-by killing spree after vowing on YouTube to slaughter women because his sexual advances had been rejected.

The spurned virgin also died from a gunshot wound to the head on Saturday after the killings were carried out while young people were out socialising in a beach-side resort near the University of California in Santa Barbara.

In a chilling video message the day before his attacks, he said he would kill every “single stuck-up blonde I see”.

Before going on his rampage, he vilified women who had spurned his advances and confessed on YouTube: “I’m 22 years old and I’m still a virgin. I’ve never even kissed a girl.

“It’s not fair. You girls have never been attracted to me but I will punish you all for it.”

Police who questioned Rodger – who suffered from Asperger’s syndrome since childhood – weeks before the killings described him as “perfectly polite, kind and a wonderful human”.

Most of his victims were believed to be university students. Six other people were injured in the shootings.

His grandfather, a British photojournalist, chronicled the Second World War, taking photos of the Blitz and West Africa.

He was the first photographer to enter the Bergen-Belsen concentration camp, an experience that led him to give up being a war correspondent.

He later founded Magnum Photos with Henri Cartier-Bresson and Robert Capa in 1947. He died at the age of 87 in 1995.

An exhibition of his photos was on show in Smarden last year.