Caldwell's two sons, ages 8 and 10, were in the home at the time of the shooting, authorities said.
Caldwell's mother, who was staying with her daughter, also was in the home at the time, according to neighbors.
Vaughn told Pennsylvania State Police Trooper Jeremy Matas, one of the first to arrive at the scene, that he shot his girlfriend inside the home, court records alleged. He told state police investigators the same thing during an interview later that night at the police station, court records alleged.
Police said the shooting was a result of a domestic dispute.
No prior criminal record was on file under Vaughn's name in Franklin County Court.
Caldwell was pronounced dead at the scene at 7:21 p.m. and an autopsy was performed Thursday in Allentown, Pa.
Franklin County Chief Deputy Coroner Jeffrey Conner said she died as a result of two gunshot wounds, but he would not say where she was shot.
Neighbor Carol Fleagle, who lives across the street from Caldwell, said Wednesday night that Vaughn knocked on the door of the Fleagle home, and when Fleagle's son answered, told him what had happened.
Fleagle said she ran across the street and into the home to check on Caldwell and found her lying on the kitchen floor.
"I'm from New York City and I've never seen anything like this in my life," said Sonja Boatman, who sold Caldwell's house to her in January.
Caldwell's death was the seventh violent death in Franklin County this year.
-- On Feb. 16, William Barbour Jr. was shot five times with a .25-caliber semiautomatic handgun after breaking into his former girlfriend's Magnolia Court home in Guilford Township, Pa.
-- Ernesto "Ernie" Casanova Jr., 17, of Chambersburg, Pa., was shot in the forehead once with a Beretta .380-caliber semiautomatic pistol after breaking into a mobile home in Green Acres Mobile Home Park in Greene Township, Pa., on April 23.
Both of those deaths were ruled justifiable by the Franklin County District Attorney's office.
-- On May 26, Memorial Day, Lawrence W. Cuff shot Janine R. Goodyear with a handgun and then shot himself at their home on Sycamore Grove Road in Greene Township, Pa.
-- Wendy Wise Schuchman, 32, of Chambersburg, was shot in the chest with a shotgun on Sept. 7 in the rear parking lot of Siggy's Food and Spirits, 454 Norland Ave.
The accused, Kevin J. Barrett, 34, of 627 Siloam Road, then shot himself in the chest but survived. He was charged with homicide and is scheduled for arraignment on Dec. 17 in Franklin County Court.
-- On Oct. 6, Charles D. Green Jr. 22, was shot in the chest with a 9mm pistol outside of his home on West Catherine Street, Chambersburg.
Bryan K. Jefferson, 37, of 226 Harris St., Harrisburg, was charged with homicide. He told police he was the person who shot Green and he turned over the gun, according to the affidavit of probable cause.
A preliminary hearing for Jefferson is scheduled for Dec. 5 before District Justice Gary Carter.
-- On Nov. 5, Chad Andrew Nace, 17, of 1 Zion Road, Newburg, Pa., in Cumberland County, was shot in the mouth with a .22-caliber rifle at a Franklin County mobile home park on Molly Pitcher Highway in Southampton Township, Pa.
Patrick Louis Traini, 15, was charged with criminal homicide. A preliminary hearing originally scheduled for today before District Justice John Weyman was postponed.