In the small lush village surrounded by fruit trees, the suspect's older brother Radmilo broke down in tears, unable to explain why the massacre had happened.
"Why did he do it? ... I still can't believe it," he said sobbing, covering his face with his hands. "He was a model of honesty."
"As a child, he was a frightened little boy. I used to defend him from other children. He couldn't even slaughter a chicken," he said.
But he said his brother had changed after serving in the army during a brutal Serb-led offensive against the eastern Croatian town of Vukovar in 1992 the worst bloodshed during Croatia's 1991-95 war for independence.
"The war had burdened him," Radmilo, 62, told The Associated Press in an interview. "He used to tell me: God forbid you live through what I went through ... Something must have clicked in his head for him to do this."
Twelve people in the village were killed immediately between 5 a.m. and 5:30 a.m. and one person died later in a Belgrade hospital, Serbian police chief Milorad Veljovic said.
"Most of the victims were shot while they were asleep," Veljovic told reporters. "The most harrowing scene discovered by police was the dead bodies of a young mother and her 2-year-old son."
Although such mass shootings are relatively rare in Serbia, weapons are readily available, mostly from the 1990s wars in the Balkans. Media reports said the suspect had a license for the handgun and police said he had lost his job last year at a wood-processing factory.
Serbian Prime Minister Ivica Dacic said the killings showed that the government must pay more attention to gun control and other social problems facing the Balkan nation, which is still reeling from the 1990s wars. His government held an emergency session and proclaimed Wednesday a national day of mourning.
Residents said Bogdanovic first killed his son and his mother before leaving his house and then began shooting his neighbors. They expressed deep shock, describing the suspect as a quiet, helpful man.
"He knocked on the doors and as they were opened he just fired a shot," said villager Radovan Radosavljevic. "He was a good neighbor and anyone would open their doors to him. I don't know what happened."
"I never saw him angry, ever," said Milovan Kostadinovic, another resident. "He was helping everybody, he had a car and drove us everywhere."
Still, neighbors said an entire five-member family was shot dead in one house, including the small boy who was the suspected killer's cousin.
Kostadinovic said the suspect was confronted by police while en route to his house.
"If they didn't stop him, he would have wiped us all out," Kostadinovic said, standing in front of his two-story, red tile- roofed house. "He shot himself when police stopped him."
His wife Stanica said their small white-and-brown dog Rocky had gotten very nervous early in the morning and was barking and jumping up and down. She said when her husband opened their door, a policewoman shouted: "Get back in!"
"He was shooting everybody. Police saved us," she said.
The suspected killer owned a gun but neighbors and his brother said he never hunted or shot weapons, even at weddings or celebrations as is traditional in the Balkans.
"He was quiet as a bug," Stanica Kostadinovic said.
Nada Macura, a Belgrade hospital spokeswoman, said the suspect had no known history of mental illness. Stanica Kostadinovic said the man's father had hanged himself when he was a young boy.
Aleksandar Stekic, 29, was fast asleep when his mother was killed. He heard the shots but "thought I was dreaming."
"When I got up about half an hour later, I found her dead on the doorstep," he told the AP.
Stekic said he went to the next house and found the same scene there, and then again in the next one.
"At that moment, I no longer knew where I was," Stekic said, adding that a policeman had handcuffed him while he roamed outside, thinking that he was the shooter.
Radoslav Stekic, 52, lives in a small white house where his mother Danica was shot dead in her bed Tuesday.
"He broke the door open and shot my mother, she was asleep," he said.
"This is where the bullet hit," he added, pointing to the bed with a brown blanket inside a small kitchen-turned-bedroom.
"She loved him more than me," he said of the shooter, who was his cousin.
Police blocked off the village while forensic teams and investigators in white protective robes took evidence from homes where the shootings took place.
Doctors said later Tuesday that the suspect's condition was critical but his wife who had called the police before she was shot was able to communicate with the hospital staff.
Serbia's last big shooting spree occurred in 2007, when a 39-year-old man gunned down nine people and injured two others in the eastern village of Jabukovac.