"Friends of the girls say their father was Egyptian and critical of popular American lifestyles." And that he was abusive.
"Friends: Murdered Teens Were Afraid Of Their Dad," by Bud Gillett for CBS 11 News (thanks to Ian):
LEWISVILLE (CBS 11 News) ― Friends and classmates are in shock after two teenage sisters are murdered, police say, by their own father.
Sisters, Amina, 18, and Sarah, 17, were each shot to death. Friends of the girls say their father was Egyptian and critical of popular American lifestyles. "I'm definitely 100% sure that it was her dad that killed her," said Kathleen Wong, a friend of the dead teenagers.
Wong says the girl's father was verbally abusive and that Sarah, especially, lived in fear. "She's always told me that she was always so scared of her dad," says Wong. "Even at school if a teacher joked around like, 'I'm gonna tell your parents about this', she would like totally flip out and start crying like, 'please don't tell'."
While Irving police won't speculate on motive they agree the family had domestic issues. "We do consider this man armed and dangerous; he does have a capital murder warrant out for him," said David Tull, Irving Police Department.
UPDATE: " She said the sisters, who wore typical American clothes, didn't talk much about their family. 'I didn't know they were Muslims until she told me they were Egyptian and Muslim,' Liz said." From the Dallas Morning News (thanks to Stacy McCain).