California police say an Iraqi-born woman who was beaten to death may have been the victim of a hate crime. The killer of Shaima Alawadi, 32, left a note reportedly reading: "Go back to your own country. You're a terrorist."

Alawadi, an immigrant, died on Saturday after the attack last Wednesday. Police said her 17-year-old daughter, Fatima, found her unconscious in the dining room of the family's home in El Cajon, California at about 11:15am. Alawadi, a mother of five, died soon after being taken off a hospital life support machine, police said.

Fatima told a local television station that her mother had been beaten on the head repeatedly with a tyre lever, and that the note said "go back to your country, you terrorist". The police confirmed a note had been found but did not release the details.

The daughter had reportedly been sleeping upstairs. She found her mother in a pool of blood with a sliding glass door into the house broken.

According to El Cajon police lieutenant Mark Coit, the family told the police that another threatening note had been found earlier this month outside their home. But they told police that they had not reported it after dismissing it as a prank.

"During the initial stages of this investigation, a threatening note was discovered very close to where the victim was found. The victim's family stated they had found a similar note earlier this month, however did not report it to authorities. Although we are exploring all aspects of this investigation, evidence thus far leads us to believe this is an isolated incident. No additional information is being released at this time," the police said in a statement.

The investigators have so far made no arrests and have not said whether they have any leads to the assailant.

The attack had been a shock to the Muslim community in the area, said Hanif Mohebi, director of the San Diego chapter of Cair, the Council on American-Islamic Relations, America's largest Islamic civil liberties group. He had been speaking to the family. "The family is still numb. They are trying to figure it all out," he said. He said there had been an outpouring of support for the family from across California and the nation.

In the wake of the 9/11 terrorist strikes, Islamophobic incidents were reported in several US cities, with attacks on people and mosques. But Mohebi said there had been little evidence of escalating tension in the area recently and there had been no incident comparable to this attack. He said a taxi driver had been severely beaten in the area a few years ago but he could recall no other recent severe physical attacks on Muslims.

El Cajon is a conservative city of 100,000 people 15 miles from San Diego that has become popular with Iraqi immigrants. The city is home to some 40,000 Iraqis, the second largest such community in the US after Detroit.

"Obviously our community is worried about this but we want to make sure we get all the facts before we do anything. Our community is pretty much in shock at this point. Hopefully the police department will bring these people responsible to justice as soon as they can," Mohebi said.

The family had only recently moved from Michigan to a house on a suburban street in El Cajon. A family friend, Sura Alzaidy, told a San Diego newspaper that the attack apparently happened after Kassim Al Hamidi, Alawadi's husband, had taken the couple's younger children to school. Alzaidy told the newspaper that Alawadi had been a "respectful, modest muhajiba," meaning she wears the traditional hijab headscarf.

Al Himidi and Alawadi migrated from Iraq to the United States in about 1993, according to local reports. Al Himidi had worked as a defence contractor in San Diego, serving as a cultural adviser to train soldiers preparing for duty in the Middle East.

"There have been hate crimes in the past but I have not seen anything like this," said Mohebi. "At the end of the day there are a very small number of people who act upon such ignorance. In general our neighbours are supportive of the community."

The murder comes at a sensitive moment for race relations in the US following the killing of a black teenager by a self-styled neighbourhood watch volunteer. Unarmed 17-year-old Trayvon Martin was shot and killed after being chased by George Zimmerman, 28, last month in Sanford, Florida, sparking a national debate about gun laws and race and calls to prosecute Zimmerman under hate crime laws.