In 1978, Dahmer committed his first murder. On June 18, he picked up Steven Hicks on Clevland Mass Road. Damo asked him if he could sit at his house for a while, since there was no one at his house and everyone else was visiting relatives. Unsuspecting, Steve readily agreed. They sat at his house for a while, drank some wine and listened to some music. At this time, Steve said it was getting late and he should go. It was this sentence that ultimately led to his murder. Dahmer later confessed that he would only kill those who tried to leave him. Throughout his life, he was always very friendly to the wanderers, but still no one wanted to stay with him, and even the people he loved eventually left him. Therefore, he believed that only if he did it himself, these people would not abandon him. Dahmer hit Steve on the head with a dumbbell and then strangled him to death on the floor. He then dismembered the body into small pieces, put it in a large plastic bag, and placed it in a slot (a space used for wiring) under the ground of his home. After a few days, the body began to decompose and emit a disgusting smell. Dahmer was worried that his family would find out when they returned, so he buried the body in the woods behind his home. A few days later, he found that some children often played there and might find corpses, so he dug them out again. At this time, only the bones were left on the body. He smashed the bones with a sledgehammer and scattered them in the woods. That way, Steve would never leave him.

The murder is virtually unknown. After this, Dahmer seemed to return to normal. But then something painful happened to him. His parents came back and told him they were getting a divorce. Because Dahmer was over 18, the court did not rule on who he had slept with. However, his parents seemed to have forgotten about him and just fought with each other for custody of David. Dahmer once again felt abandoned, and this time it was his parents who didn't want him. Eventually Joyce and David moved to Chippewa Falls, Wisconsin, while Dahmer remained at his original home with his father. Damo ran away for a while and brought back a new girlfriend. Dahmer then attended Ohio State University in Columbus. But he didn't even stay for one semester and joined the army in December 1978. He was first stationed in Baumholder, Germany, and then returned to the United States. In March 1981, he was discharged from the army for being an alcoholic and excessively depressed. By 1982, he moved to West Allis, Wisconsin, to live with his grandparents. Now life seems to be taking a turn for the better, and Damo even plans to fall in love and start a family. But he was soon detained for exposing himself in the market. In 1985, he found a job at the Ambrosia chocolate company, where he was arrested a year later for urinating in public.

After this, Dahmer once again felt the temptation to kill. In September of 1987, Steven Tuomi traveled to Milwaukee from Ontonagon, Michigan to have some fun. He passed by Dahmer and chatted for a while, then they went to a motel and drank a lot. When Damo woke up, he found Steven dead with blood pouring from his mouth. He then put the body into a suitcase and took it back to Damo's grandmother's house. There, Dahmer had sex with the corpse, masturbated in front of it, and then dismembered him like a cow with a butcher knife. Four months later, Damo picked up another 14-year-old boy. He still took him to his home and killed him in the basement. The cause remains the same. The boy's body was later almost impossible to identify because it was so badly decomposed. It was not until after Dahmer was arrested that his identity was revealed. By March 1988, just two months later, Dahmer killed Richard Guerrero again.

Richard was preparing to go to a friend's house to play. Dahmer met him on the way, took him back to his home, and killed him.

During this time, Dahmer's grandmother began to dislike him. Because his behavior was so strange, she asked him to move out. She later told police he spent a lot of time in the basement and that there was always a disgusting smell. She kept hearing Dahmer knocking on something there all night. So she told Dahmer that she could no longer be his nanny. Damo was very sad because his grandmother once again abandoned him. In 1988, he moved to the Oxford Apartments on 25th Street in the North End. As a result, he was soon arrested for molesting a boy there.

In March 1989, Dahmer met Anthony Sears (Anthony Sears) at the LaCage bar. This bar is a gay men's hangout bar. Damo often comes here to play. Dahmer told Anthony they could hang out at his house, drink, take nude photos and have sex. Anthony readily agreed. They returned to Dahmer's grandmother's house, and after having sex, Dahmer put some homemade sleeping pills into a wine glass. After he fell asleep, Dahmer chopped him open and began the same routine. But this time he boiled Anthony's head in water, peeled off his skin, and after it dried, he painted the head gray and took it home as a souvenir. In May, Dahmer was sentenced to three years in prison for second-degree sexual harassment and luring a boy for immoral purposes, which was later reduced to one year of volunteer service and five years of probation. The court banned him from having contact with children under 18.