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.
Sabina Niksic contributed from Bosnia.