BONNE TERRE, Mo. (AP) -- The man police say burst into a Missouri duplex apartment and killed three people before fatally shooting himself was distraught over his breakup with one of the victims, the man's sister said Wednesday.
Police said 25-year-old Nathan Fortner broke into the home Tuesday and killed his former girlfriend, 19-year-old Danielle Bement, along with Bement's mother, Christine Snider, 37, and Snider's live-in boyfriend, Derek Nash, 32. Snider and Nash lived in the duplex, and Bement had been staying there. Two boys at the home were unharmed.
Meanwhile, a 20-year-old woman who was an acquaintance of both Fortner and Bement was found dead Tuesday in neighboring Washington County. Authorities suspected her death was connected, but were still investigating.
Fortner's sister, Angie Fortner, said Nathan Fortner was unemployed, bipolar and overcome with despair over the breakup with Bement. The couple's 18-month-old son was found unhurt Tuesday in the same sport utility vehicle as his fatally injured mother.
Angie Fortner said her brother left three Post-it notes at her house.
"We will never get back together and it hurts so bad I just can't take that," read one. "I know you all are going to be very mad at me but I just can't take it anymore," read another.
In the third note, Fortner expressed his innocence in a pending rape case against him.
Angie Fortner said her family wanted to express their sorrow to relatives of the victims. Her brother, she said, "was a good person. He loved his kid. He would do anything for his kid. I don't know what happened."
She said Fortner was on medication for bipolar disorder, but had stopped taking the medicine. "We didn't discover that until yesterday," she said.
The killings left people shaken in Bonne Terre, a former mining community of 7,000 residents that sits about 55 miles southwest of St. Louis.
Bonne Terre Police Chief Doug Calvert said officers were still investigating the motive.
"I have no idea what was in his mind," Calvert said. "Somebody who could commit a crime this horrible, I could only speculate."
Police first received a call Tuesday morning that a man was trying to break down the door at the duplex on a quiet and secluded cul de sac. Calvert responded. As soon as he arrived, he received a chilling call from his dispatcher.
"They said, `shots fired, chief, shots fired,"' Calvert recalled. "Then I saw the male subject running away."
Other officers arrived and confronted Fortner about 500 feet away as he ran toward a wooded area not far from North County High School. Fortner turned the handgun on himself. He died instantly.
Back at the duplex, Calvert found Nash dead in the doorway and Snider dead in a bedroom. A 3-year-old boy was in the house but not physically harmed.
Police soon found Bement in the SUV with her son, where she had apparently been trying to protect the boy. She was alive but died at a hospital a short time later.
The body of the 20-year-old woman was found just outside a home near Bismarck in Washington County. St. Francois County Coroner Jim Coplin said it appeared her death was connected to the others. Missouri State Highway Patrol Sgt. Al Nothum said state investigators weren't yet willing to make that connection, and were still investigating.
The woman was reported missing Monday night. Her name was not released.
Calvert said an 11-year-old child also lived in the Bonne Terre apartment but was at school at the time of the killings. He wasn't sure of the relationships of the 11-year-old and 3-year-old. All three children were put in the care of the Missouri Division of Family Services.
"The 18-month-old is probably too young to remember, but I worry about what the 3-year-old will remember," Calvert said.
Fortner's Facebook page lists him as engaged to Danielle Bement. He posted this message on his Facebook wall at 4:57 a.m. Tuesday, just hours before the shooting: "Just trust n god n u will go a long way and never trust no one I love u cameron."
Police in another neighboring town, Farmington, believe Fortner stole a handgun from a residence there. Calvert said it apparently was the one used in the shootings.
Fortner was scheduled to go to trial in April on a 2008 rape charge. He was free on $150,000 bond.
It was the latest of several criminal charges against him, according to Missouri's online court reporting system.
He was arrested in July 2003 and charged with burglary, property damage and tampering with a motor vehicle. He pleaded guilty in 2004 and received five years of probation.
In 2006, Fortner pleaded guilty to third-degree assault and disturbing the peace. He was again placed on probation.
Jesse Smith, 30, said he lives across the street from the Bonne Terre duplex, but left for work before the shootings. Smith said he frequently saw Bement quarreling with a man.
"I saw them arguing a million times," he said.
But Calvert said that contrary to earlier reports, police had never responded to a domestic disturbance at the duplex.
(Copyright 2010 by The Associated Press. All Rights Reserved.)