UPDATE 8:15 p.m.:

For hours, bloggers debated whether the murders of two teenage sisters in Texas were "honor killings" (see updates below, beginning at 3:50 p.m.) and now this:

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'." (Emphasis added)

UPDATE 9:40 p.m.:

A commenter at Atlas Shrugs links to Amina's Myspace page, where the music is "No One" by Alicia Keys and Amina's personal quote is:

"Do not take life too seriously. You will never get out of it alive."

* * * MORE UPDATES BELOW * * *

Sara A. Carter reports today that law enforcement has begun to take seriously a trend that bloggers have been warning about:

Sympathy for al Qaeda has produced "sudden jihad syndrome" in domestic terror cells unaffiliated with foreign terrorists and people seeking to carry out attacks in the U.S., a law-enforcement intelligence analysis says.

The Dec. 6 report by the Texas Public Safety Department's Bureau of Information Analysis warns officials not to dismiss individual or homegrown terror cells as "wannabes," saying they pose a credible threat to homeland security.

"Oftentimes, these attackers are dismissed as suffering from mental health issues, but their own words and writings reveal an affiliation with Islamic supremacy or an affinity for Islamic extremism," said the report, which was distributed to federal, state and local law enforcement in Texas. "As a result, law enforcement should not be too quick to judge their attacks as having no nexus to terrorism."

The report, a copy of which was obtained by The Washington Times, cited al Qaeda theorist Abu Mu'ab al Suri's book "Call to Global Islamic Resistance," in which Mu'ab al Suri noted that the future of al Qaeda terrorist fighters will depend on individual and small-group terrorists.

That was when a just-graduated student named Mohammed Reza Taheri-azar, 22, and an Iranian immigrant, drove a sport utility vehicle into a crowded pedestrian zone. He struck nine people but, fortunately, none were severely injured. . . .

Taheri-azar represents the ultimate Islamist nightmare: a seemingly well-adjusted Muslim whose religion inspires him, out of the blue, to murder non-Muslims. . . .

This is what I have dubbed the "Sudden Jihad Syndrome," whereby normal-appearing Muslims abruptly become violent.

The blog reaction to Sara Carter's story today ranges from scoffing (Wonkette) to serious, including Howie at The Jawa Report:

Since the war on terror, al-Qaeda has taken a lot of damage. This results in what we call al-Qaeda 3.0. Small independent cells of sympathetic Islamic radicals willing to carry out what they believe are al-Qaeda central's wishes. Many of the kidnappings of journalists in Palestine last year are examples of this type of activity.

In other words, the writings of Islamists may be sufficient to push some susceptible individuals to act upon the ideology of Islamic radicalism expressed by terrorist groups. Having pulled an ideological justification from extremist sources, their actions should not be seen as isolated, but are instead a part of the global jihad being waged by the likes of bin Laden. In other words, look for more cases of homegrown terrorism linked by ideology, not direct command-an-control, to radical groups abroad.

UPDATE 3:50 p.m.:

Speaking of Texas, Atlas Shrugs highlights a double-murder near Dallas that she says is a suspected "honor killing":

Lewisville police officers and Denton County SWAT officers have surrounded the home of a man accused of killing his two teenaged daughters. . . .

At about 7:30 Tuesday night police got a cell phone call from a woman saying she had been shot, but didn't know her location.

An hour later police responded to a suspicious vehicle call in a parking lot and found two young women dead of gunshot wounds inside the car.

Investigators have identified the two as 17 year-old Sarah Yaser Said, and 18 year-old Amina Yaser Said.

-- RSM

UPDATE 4 p.m.:

Pamela at Atlas Shrugs e-mails to call attention to archives of her previous blogging on "Lone Jihadi a/k/a Sudden Jihad Syndrome."

-- RSM

UPDATE 6 p.m.:

Are the Texas murders an "honor killing"? Some bloggers are hesitating to call it that. The Jawa Report calls it an "apparent honor killing," and Ace of Spades also employs "apparently" as a modifier.

The Fort Worth Star-Telegram has police saying a "domestic issue" may be the motive, but add: "Investigators did not describe the domestic issues or say who was involved." A joint report by WFAA-TV and the Dallas Morning News has this:

Police are also looking at the motives which may have led Said to possibly murder his two teenage daughters, one of whom called 911 from a cell phone near the spot where the girls were later found.

Police say they are looking into the possibility that the father was upset with his daughters dating activities.

"It's something well worth looking into," said OFC David Tull of Irving Police. (Emphasis added)

-- RSM

UPDATE 6:15 p.m.:

Robert Spencer of Jihad Watch is cautious about suspicions of an "honor killing":

Now, of course, that may turn out not to be the case. But it is good to see that the possibility is being investigated, for in a world where some Muslim parents consider honor killings fully justified, and the Jordanian Parliament rejects on Islamic grounds a law stiffening penalties for honor killings, it cannot be lightly dismissed.

UPDATE 6:25 p.m.:

Bryan Preston at Hot Air:

It could still turn out that the man is simply crazy for reasons unrelated to the girls' dating activities, though we've been through enough of these stories now to have reason to think it's not simple craziness that led to this.

-- RSM

UPDATE 6:50 p.m.:

Debbie Schlussel invites her readers to play "Guess the Religion."

-- RSM

UPDATE 8:35 p.m.:

Jammie Wearing Fool also blogged the story today. Ace of Spades has an update.

-- RSM

UPDATE 9:05 p.m.:

Robert Spencer updates at Jihad Watch, and Bryan Preston updates at Hot Air.

-- RSM

UPDATE 10:15 p.m.:

The Dallas Morning News confirms the girls' family is Muslim:

Friends describe Amina and Sarah as quiet but well-liked students at Lewisville High School. They played tennis and soccer and were enrolled in many Advanced Placement classes.

"They were extremely smart -- like geniuses," said Allison Villarreal, a senior at Lewisville High, where Amina was a senior and Sarah was a junior.

Liz Marines, secretary of the Lewisville High School Student Council, had classes with both of the sisters and also remembers their scholastic abilities.

"Amina was very nice with everybody. She helped me in [Advanced Placement English] class," she said. Sarah was a sophomore when she took an Algebra II class with Liz, who was a junior at the time.

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.

UPDATE 10:45 p.m.:

Credit where credit is due: The 10:42 a.m. timestamp on Debbie Schlussel's post makes her the first blogger to comment on this story, as far as I'm aware, and she immediately characterized the crime as an "honor killing."

Dallas Morning News columnist Rod Dreher at BeliefNet started blogging the story at 12:15 p.m.

-- RSM