The most frightening aspect of the movie Se7en is not the grisly murder victims, although those scenes are some of the most disturbing I’ve ever seen. The scariest thing about this movie is the ease with which John Doe is able to understand people and get into their heads and subsequently plan his actions for maximum impact.
With each of the murder victims, it is revealed that Doe researched them before he selected how they would die. In the case of sloth, he kept the victim barely alive for a year, making sure the drug dealer and child molester would be a prime example of laziness. When he enacted the sin of lust, both the prostitute who was raped to death and the man Doe forced to commit the murder were victims who would suffer for their sin. Doe knew the man he selected could be forced to kill the woman out of a desire for self-preservation.
The gluttony and pride victims were selected because they exemplified the sins they would die for in ways that made it easy for Doe to use them. He understood that the model had so much pride in her physical appearance that she would rather die than lose her good looks. The lawyer who was guilty of greed was also carefully chosen by Doe, largely due to his defense of a previous client, the victim of sloth. Doe knew how to read each of these victims and used his knowledge of human psychology to create the largest impact possible through their murders.
This knowledge of what makes human beings tick is especially frightening as Doe applies it to the detectives who are looking for him. As he embarks on his quest to teach humanity to look at the sins it portrays, Doe had no idea of who would be sent to investigate his crimes. When he encounters Mills and Somerset and gets to know more about them, he immediately understands how they can fit into his larger picture.
In Somerset, the jaded veteran detective, Doe understands he has a sort of a kindred spirit. Somerset is already in agreement with Doe that the world is a terrible place. The detective has retreated behind a wall of non-caring and a refusal to invest any personal feelings into much because of the state of the world. Somerset is the choir to which John Doe doesn’t need to preach.
Mills, on the other hand, is immersed in caring about life. He attacks his new job as detective in the big city with enthusiasm, even through the grisly crime scenes. He wishes to start a family with his wife, despite the increasing problems of the world surrounding them, which would provide the back drop for raising the child(ren). Mills is the one of the two who would be most affected by a direct attack from Doe, so he is the one Doe selects to help him showcase the two last two sins on his list, envy and wrath.
By killing Mills’ wife and then taunting the detective with the crime, Doe knows what the outcome will be. He understands that Mills has enough zest for life and passion within him that he will kill Doe for what he did. The same reaction would not have been garnered from Somerset.