
## 4.3 Social Network Visualization

A social network diagram is drawn from the observed records according to the process in figure 2. The unobserved person in a suspicious record is drawn as a red node. 

The red node and the gateway persons ( , ) i j pgtw b c **are connected with red links.** 
Figure 10 shows the social network diagram. The condition is the same as in figure 5, where a covert conspirator, Mustafa A. Al-Hisawi, has been hidden and the target to discover. The 4 terrorist groups are inter-connected with 10 of the highly ranked red nodes, DEi, corresponding to Mustafa A. Al-Hisawi hidden in the suspicious records. The bottom left cluster, including Nawaf Alhazmi, Mohamed Atta, and Hani Hanjour, is isolated and not connected to the red nodes. Terrorists who appear more frequently are less emphasized because of the denominator of eq.(5) or eq.(6). This is not a problem, but good news. We are inclined to overlook uncommon and unexpected clues by paying too much attention to something frequent and conspicuous. On the other hand, focusing on something infrequent is a double-edged sword. We may confuse the clues observed infrequently with random noise. Majed Moqed, Mohamed Abdi, and Ahmed K. I. S. AlAni are probably noise. They are distant from Mustafa A. Al-Hisawi in figure 4. 

It is, however, remarkable that Waleed Alshehri and Mohand Alshehri are retrieved as neighbor persons of the red nodes indicating the existence of Mustafa A. Al-Hisawi. They are close to him. Waleed Alshehri, one of muscle hijackers, helped Mohammed Atta hijack the AA11 and fly it into the North Tower of the World Trade Center. Mohand Alshehri hijacked the AA175 and flew it into the South Tower of the World Trade Center. Waleed Alshehri is connected with 6 links. He is the keystone person for the investigators to gather information on relatives, friends, and associates to approach to Mustafa A. AlHisawi. 

![0_image_0.png](0_image_0.png)

