I just attended a bloggers conference with Lt. Col. Avital Leibovich of the IDF. She didn't shed too much new light on the attack.
She said, "An hour ago, we had a severe terroristic attack at - which is very close to Hebron. The info we have is that it was a civilian car. Four people that were sitting inside the car were killed, amongst them a pregnant woman. This is a very severe terroristic attack. In the past two or three years, the security situation in the WB was overall stable and this is such a vicious attack on civilians. We wish that this security situation will not deteriorate."
She noted that while it was the third terror attack in the West Bank this year, it was the first one against civilians. Things had been pretty calm in the area for a while, or, as she said, "the security situation had not deteriorated."
I asked if any of the roadblocks/checkpoints that had been removed recently would have helped. She sidestepped the question, saying that the IDF took orders to remove the roadblocks from the government, and that over 180 roadblocks had been removed over the past couple of years, noting that she could drive from Jerusalem to Hebron without stopping at a single checkpoint. The situation had been stable up until now.
The IDF had no information yet on who was responsible, what kind of weapons were used, nor did they confirm that reported scenario that the terrorists stayed to confirm their kills.
The security level was not raised in Israel in anticipation of any attack before the Washington talks begin; they raise the levels based on intelligence information and there was apparently no warning of this attack. There is increased security in the area now as they try to catch the murderers, but there has not been a general raising of security as a result of this attack.
(h/t MW for first paragraph)