I will let you make up your own mind on what he was because I say he was a Christian.
The Religious Affiliation of Milwaukee Serial Killer
Jeffrey Dahmer
Jeffrey Dahmer was one of the most infamous and notorious serial killers in American history. Part of the reason he became so well known was the number of victims he killed: at least 17 young men and teenage boys between the years 1978 and 1991. Another reason for Dahmer's infamy was the peculiar nature of his killings. He stored the body parts of many victims in his apartment. He also engaged in cannibalism, although the extent of this is less than was widely believed after this detail was sensationalized in media reports. Dahmer's killing spree was finally discovered and halted in 1991 when one of his intended victims was able to escape and lead police to Dahmer's apartment, where the remains of 11 bodies were found.
Dahmer was born into a family of devout members of the Stone-Campbell denomination known as the "church of Christ" or "Churches of Christ." He was an active
churchgoer until the age of 5. After that, Dahmer was never again actively religious or a regular churchgoer until after his arrest and imprisonment. After being imprisoned for his crimes, Dahmer sought out the church of his childhood and petitioned to be re-baptized in the Church of Christ. This caused some controversy, but he persisted until he was able receive this rite, which he was apparently sincere in requesting. Shortly after being re-baptized into the Church of Christ, Dahmer was murdered by his cellmate.
Jeffrey Dahmer's religious affiliation as a member of the Stone-Campbell denomination known as the Church of Christ is unusual. We are aware of no other members of this denomination who were famous serial killers. Jeffrey Dahmer's homosexuality, on the other hand, is not unusual among serial killers. The fact that Dahmer was a homosexual, as were most or all of his victims, was widely publicized at the time of his arrest and trial. Prior to his arrest, Dahmer was active in the Milwaukee gay community, although the word had reportedly spread through this tight-knit GLBT community that Dahmer was a person who should be avoided. Other well known homosexual or bisexual serial killers include Andrew Cunanan, John Wayne Gacy, Patrick Wayne Kearney, Gilles de Rais, Randy Steven Kraft, Michael Swango, Andrei Chikatilo, David D. Hill, Wayne Williams, Larry Eyler, Henry Lee Lucas, Fritz Haarmann, and dozens more. It is not clear why Dahmer became associated with homosexuality in the public consciousness more than many other serial killers, including many whose victims outnumbered Dahmer's. This may simply have occurred because homosexuality was a more widely-discussed topic in public media at the time of Dahmer's arrest. Certainly most homosexuals are law-abiding individuals, and Dahmer's sexual identity was not a direct cause of his violent behavior.
Although there was much disagreement among expert witnesses and psychologists who testified in Dahmer's trial, there seemed to be a general consensus that Dahmer harbored some type of hatred toward homosexuals. Although there was clearly a sexual component to his killing, as his victims were generally his sexual partners as well as his murder victims, experts generally agreed that Dahmer had control over his actions and that his murders were not purely a result of sexual compulsion or aberrant sexuality. Some people have speculated that Dahmer's Biblical religious background may have contributed to a negative view of homosexuals, which in turn contributed to a negative self-image and a hatred of himself and other homosexuals, which in turn led him to become a serial killer. Whether or not this is what happened is unclear. One problem with this theory is the minimal exposure Dahmer had to organized religion during most of his life. Another theory (also far from certain) holds that Dahmer felt rage toward the gay community for their lack of acceptance of him. Far more likely than either of these theories is the notion that the reasons Dahmer became a serial killer are essentially the same reasons that have caused other people to become serial killers.
http://www.adherents.com/people/pd/Jeffrey_Dahmer.html