In between, there were victims in Rockville, Maryland; Savannah, Georgia; Atlanta; and Nassau County, Florida.
In each case, Bowles had a signature: He stuffed the victims' throats with objects — towels, rags, toilet paper, dirt, leaves and even a sex toy.
Bowles did not say anything before his execution, but said in a handwritten statement dated Thursday that he was sorry for his actions.
"I'm sorry for all the pain and suffering I have caused. I hope my death eases your pain," Bowles wrote.
"I want to tell my mother that I am also sorry for my actions. Having to deal with your son being called a monster is terrible. I'm so very sorry. I never wanted this to be my life. You don't wake up one day and decide to become a serial killer."
The execution itself proceeded with nothing unusual happening, other than Bowles speaking to himself perhaps in prayer before the procedure was carried out.
Investigators say if he hadn't been caught, he would have kept on killing.
"He probably enjoyed it after a while," said Thomas Youngman, a Daytona Beach detective assigned to the Roberts murder.
"Why do you kill people after the first one? The first one could be a mistake, maybe. But then the second, all right, I'll maybe give you that. But the third, fourth fifth and sixth? When do you stop?"
It wasn't hard for Daytona Beach police to figure out who killed Roberts, the first victim in March 1994: Bowles left a probation document at the scene and also was caught on an ATM camera trying to withdraw money from Roberts' account.
What proved more difficult was capturing him, something they were unable to do until after five other men in three states had been slain.
Bowles, 57, was raised in West Virginia, where he experienced drugs and violence at a young age.
His father was a coal miner who died of black lung before he was born.
His mother remarried multiple times, and his first two stepfathers were abusive, according to court records.
His mother and brother testified that Bowles began drinking, smoking marijuana and huffing glue when he was 11 years old.
When he was 13, he fought back against his second stepfather, smashing a rock in his head and nearly killing him, according to court records.
That's when Bowles left home.
Investigators say Bowles survived by letting gay men perform sex acts on him for money, though he has maintained he is straight.
"I had a question about him being gay. He told me he was not, and I said, 'What do you describe yourself as?' He said, 'A hustler,"' Youngman said.
"He'd befriend these old guys and have sexual relations with them, but I think they performed on him. He said he did not perform on them."
He also had a history of violence against women.
He was convicted of beating and raping his girlfriend while living in Tampa in 1982 and sentenced to eight years in prison.
The victim had severe injuries, including tears on her vagina and anus.
Former Savannah detective John Best remembers hearing details of the crime as he investigated the murder of 72-year-old World War II veteran Milton Bradley.
"The Tampa detective, I remember her exact quote, 'I've seen better looking bodies in an autopsy,"' Best said.
Best still suspects that Bowles is bisexual and also believes he might have killed women.
He said during an interview with detectives, Bowles freely admitted to killing his male victims, almost in a boastful manner, but when asked if there were female victims, he hemmed and hawed.
"He never gave us a yes or no answer," Best said.
"It was, 'Let's change the subject."'
-AP
