Zohair Zaidi, identified as a friend of Sarah's, told the Dallas Morning-News that Yaser Abdel Said had recently threatened Amina after discovering the teen had a boyfriend.
"He told Sarah, 'I'm going to put a bullet through Amina's head, and you better get used to her because she's not going to be around much longer,'" Zaidi told the paper, citing a conversation she had with the younger of the two sisters.
Police say they originally received a 911 call, from one of the two sisters New Year's Day at 7:33 p.m. The young woman told the dispatcher she had been shot, but could not tell police where she was or who had shot her.
An hour passed between the first 911 call and a subsequent call to police made by a staff member at the Omni Mandalay Hotel in Irving reporting that two women were passed out in a cab at the hotel's taxi queue.
Authorities, who were in the area after tracking the cell phone signal from the 911 call, arrived to find the sisters dead inside a cab that Yaser Abdel Said had been driving. Each had been shot multiple times and their father was missing.
"We don't know how he left the scene," Tull said, adding that it may have been by foot or by car. A SWAT team entered the Said house the following day, but failed to find the suspect.
Authorities have obtained an arrest warrant for Said on two capital murder charges and are now working with state and federal investigators to find the wanted man. A $10,000 reward has been offered for information leading to Said's indictment.
Said is described as 6 feet 2 inches tall, with black hair and brown eyes. Police believe Said may be carrying a handgun.
In December, religious tension played a role in the murder of Aqsa Parvez, a 16-year-old who police say was strangled by her father, Muhammad Parvez, also a cabdriver. Part of that dispute reportedly had to do with the teen's resistance to wearing a traditional "hijab" or a head scarf.