Causes

Until now, it is unknown what is the direct cause to the disorder; however, some studies might have discovered the connection between the disorder and some disabilities which cause pedophilia.

Facts:

In 2002, researches conclude that there’s a connection between pedophilia and lower IQ (approximately 10 points lower).
Lower memory ability.
Pedophilia is related to physical height, which some of them has shorter 1 inch than other adults.
Inherited genetic factors are not the cause of the development of the disorder.
Have lower activity in the hypothalamus when compared to other adults
Blanchard, Cantor, and Robichaud (2006) stated some evidence indicates that some of pedophilic men might have less testosterone.
30 percent of pedophiles are left-handed and ambidextrous.
Tumor in the brain could make pedophilic activity. In a case, a teacher in Virginia became interested in child pornography and was caught because he molested his stepdaughter. A night before the sentencing of him, he had a bad headache and went to an emergency room. MRI showed that there’s tumor in his brain. The doctor then removed the tumor, and his “obsession” with child faded. (Zarembo, "Many researchers taking a different view of pedophilia")
Pedophiles might also have been harassed and abused during their childhood, which leads to trauma. By molesting other children, these pedophiles “attempt to re-live the trauma they experienced and they learn how to master it” (Downey, "Inside the Mind of a Pedophile")

Internal causes:

Might have suffered injuries in their head before and resulting unconsciousness.
Disruption on the connective circuitry of the brain.
Cerebral dysfunctions including cognitive distortions (Scott, 1984)
Early neurodevelopmental perturbations (Schiffer, 2008). Studies showed that the disabilities and abnormalities occur at the front and center of the brain. Moreover, it decreases the volume of gray brain in the central striatum. Furthermore, the nucleus accumbens, orbital fronal cortex, and cerebellum are affected. Those areas are important because it controls human's behavior.

External causes:

Abused/Harassed by adults during childhood.
Having a family problem and traumatic experience during childhood.