Dennis Rader, 59, a married father of two and a former church leader, was arrested in Wichita, Kansas, in connection with at least 10 murders dating back to 1974.
BTK - a self-coined nickname for "Bind, Torture, Kill" - sent rambling letters to the media.
In one, he asked: "How many do I have to kill before I get my name in the paper or some national attention?"
Mr Rader was arrested after his daughter, Kerri, 26, reported her fears that her father might be the killer. Police asked her for a voluntary blood sample. They found it was a 90% match with BTK. They then placed Mr Rader, a former scout master, under surveillance. They said they had detained him "without fuss" after pulling him over in his car.
He had worked for more than a decade as a municipal compliance officer in nearby Park City, in charge of reporting on those accused of violating local laws and other nuisances.
Although no charges have yet been filed, Wichita's police chief, Norman Williams, said: "The bottom line: BTK is arrested." This prompted applause from a crowd that included relatives of some of the victims.
Police say they plan to file 10 counts against Mr Rader in connection with killings between 1974 and 1991 - eight of first-degree murder and two other homicide charges.
BTK first gained notoriety in the mid-1970s with seven murders in five years. His first victims were a 38-year-old retired air force mechanic, his wife and two of their children, who were murdered in their home. While his victims appeared to be chosen at random, his method of murder was consistent.
He would cut telephone lines, break into homes, tie up his victims and force them to suffer a slow death.
He seemed to have disappeared in 1980, raising speculation that he had either died or moved on. However, he re-emerged last March, strangling a 28-year-old woman, Vicky Wagerle, and sending a letter, signed BTK, with a copy of her driving licence and photographs of her body, claiming responsibility for her murder.
"It is possible something in his life has changed. I think he felt the need to get his story out," said Richard LaMunyon, Wichita's police chief from 1963 to 1989.
Relatives of the victims expressed a mixture of relief and revulsion at the arrest.
Jeff Davis, the son of Delores Davis, whose body was dumped in a rural area after she had been murdered at home, said: "Probably the lingering emotion is revulsion.
"It's going to take a while to reconcile the fact that my mom spent her last minutes on this earth at the hands of the lowest form of social sewage on the ladder of evolution. It's hard to accept that's what she last saw before she died."