A fellow death row inmate, a "nice boy" who calmly murdered his parents and called the police. He's highly educated and intelligent, and constantly corrects Perry's grammar. He drives Perry nuts. He's been diagnosed as a schizophrenic, but his insanity defense wasn't successful. He was hanged three years before Perry and Dick.
She's the wife of a farmer who thinks the world of Herb Clutter, who helped her family out when they moved to Holcomb. She's so upset by the murders that she and her husband decide to move out of state. Herb nominates her for an award at a 4-H meeting because she's so helpful to her neighbors. She represents the damage done to the community by the fear resulting from the murders.
Don knew Perry when he was in the service. Until he found religion, Don wasn't much more law-abiding than Perry. When he hears about the murders, he feels it's his Christian obligation to reach out to Perry and try to save his soul. He doesn't have much luck, but Perry's grateful for his friendship and his visit to the jail. He testifies at the trial about the need for Christian forgiveness but isn't any luckier there.
The two surviving children of Herb and Bonnie. They return to Holcomb as soon as they hear about the murders, as do many of the family members who were planning to celebrate Thanksgiving in Holcomb. They stay for a few days afterwards, since Beverly and her fiancé decide to move up the date of their wedding because so many family are already in town.
Lots of characters are involved in the trial—attorneys, witnesses, judges, psychiatrists, appellate lawyers. We get to see the wheels of justice turning—very slowly—as the case goes through many appeals and stays of execution. Capote is great at showing how the different professionals see the case from different perspectives. Things can get pretty hot in that courtroom.
Alvin's wife is the daughter of an FBI agent, so she knows what her husband's going through. She gives us an inside look at how his personal life was affected by the case. She tries to make sure that he has a comforting home to return to after long stressful days on the case.
In the aftermath of the murders, many family friends help with cleaning up the house and doing what they can to help with the investigations. They're mentioned in the book as a way of portraying the close-knit community and to illustrate how well-liked this family was.
These women give us a good idea about how the news about the tragedy spread through the town and what kinds of opinions and gossip were developing. The Postmistress, the café owner, the other women—they're the Greek chorus commenting and tracking the action.
Larry's a local English teacher who was at the Teacherage when Nancy Ewalt and the Kidwells came in hysterical after finding the bodies of the Clutters. He went back to the Clutter house with them and the sheriff, and decided he should take notes about what happened in case he ever had to testify in court. We never really learn anything about Larry, but it's he who provides the eyewitness details of the crime scene as they travel through the house and discover the bodies.
Sue Kidwell is the source of information about part of Nancy's last day, since they have a lengthy phone call about Nancy's relationship with Bobby. Sue is Nancy's inseparable best friend since childhood. She's one of the few people who feel entitled to give Nancy advice about her romance with Bobby. Sue's father left the family when she was young, and the Clutters kind of adopted Sue and her mother.
Sue and Nancy Ewalt are the ones that first find Nancy's body after no one answers the phone on the Sunday morning after the murders. Nancy Ewalt had been dropped off to drive to church with the Clutter family, and when her knock went unanswered, she and her father drove to where the Kidwells were living. On returning to the Clutter home, the two girls walked upstairs to Nancy's room and found her body. Both girls testify at the trial about the horrible sight of their friend's bullet-ridden body.
The wife of the Undersheriff of Finney County, she takes care of the prisoners while they're in the county jail, cooking and sewing for them. She befriends Perry and sees him as a sad, lost soul. She makes an elaborate meal for him and his visitor Don Cullivan. She's portrayed as extremely kind and compassionate.
Bobby is Nancy Clutter's boyfriend. They've dated for many years, and he's crazy about her. He's proud that the most popular girl in school chose him. He's a nice boy whose only flaw seems to be that he's a Catholic and not a Methodist. He's at the Clutter home until around 10 on the night of the murders, watching TV with Nancy and her family, something he often does. He'd asked if they could go to a movie until midnight, but Mr. Clutter vetoed the idea. It haunts Bobby that if Mr. Clutter had allowed them to go, maybe Nancy would still be alive.
When the bodies are discovered, he becomes the prime suspect but passes a lie detector test. He's devastated by Nancy's murder and eventually can't even handle hanging out with Nancy's friends. He's creeped out at the thought that the murderers may have even been hiding in the dark when he left that night. As a character, his main function is to illustrate an important part of Nancy's life.
Stoecklein's a quiet hired man who lives on the Clutter property with his small family. He was up with a sick baby the night of the murders. He claims not to have heard anything that night. He knows that people in town have been talking about him as a possible suspect and wishes they'd "stop yappin" (2.5) about it and realize why he might not have heard the shots. Stoecklein helps Herb's friends burn the bloody clothing and mattresses from the home.
He and his wife can't stand the idea of remaining on the property out in the middle of nowhere. They're as terrified as anyone about the murders and quickly decide to move to a house closer to the road.