Richard Baumhammers, 34, of the Pittsburgh suburb of Mount
Lebanon, had named himself chairman of The Free Market Party, which he described as a pro-European American group.
Mr Baumhammers - whose parents emigrated to the United States from Latvia - allegedly killed his Jewish neighbour, two Asian men in a Chinese restaurant, an Indian-born grocer and a black karate student.
He is also accused of shooting into two synagogues and spray painting a swastika on one.
Mental illness
Lieutenant David Walsh of the Allegheny
County Police Department said Mr Baumhammers was trying to recruit members to The Free Market party "anywhere he could get someone to sit and listen".
Mr Baumhammers had a history of mental illness and had been placed in the psychiatric unit of a Mount Lebanon hospital last year for more than a week after he complained that he had been poisoned during a trip to Europe, police said.
Mr Baumhammers qualified as a dental surgeon and was a professor at the University of Pittsburgh's School of Medicine.
He described himself as both an international and immigration lawyer, but appears to have done little legal work in recent years.
Mr Baumhammers' attorney, William Difenderfer, has said that his client has a history of mental illness, but refused to elaborate.
"It is way too early to say anything," he said.
Mr Baumhammers is now being kept under suicide watch at Beaver County Jail.
Funeral
On Sunday, about 700 people gathered at a Hindu temple to remember Anil Thakur, 31, one of the men gunned down at the Indian
grocery.
Another man, Sandip Patel, 25, remained hospitalised in a critical condition.
"The Indian community stands strongly united in condemning this violence," said Vinod Shah, the chairman of the Hindu Jain Temple in Monroeville.
"We cannot forget our belief in nonviolence."
The attacks came two months after another shooting rampage in the Pittsburgh suburbs.
On 1 March, Ronald Taylor, who is black, allegedly killed three white men and wounded two others.
Police said they found hate writings in Mr Taylor's apartment expressing harsh opinions of Jews, Asians, Italians and the media.