44-year-old Gregory Twyman was arrested Tuesday afternoon.
Prosecutors say Twyman shot and killed 37-year-old Jamica Woods shortly after noon at the couple's home on Rokeby Road in East Fallowfield Township.
Woods was Twyman's longtime girlfriend. The two have a daughter together.
After the shooting, prosecutors say Twyman called 911 and told police he had shot his girlfriend to death with a shotgun. When officers arrived, they found Twyman on the front porch smoking a cigarette. They arrested him.
Inside the home, officers found Woods dead from multiple gunshot wounds. They also found the murder weapon, a single shot shotgun that has to be reloaded to fire more than one time.
In a statement released Wednesday, Chester County District Attorney Tom Hogan said, "This is another example of domestic violence accelerating into a murder. A mother is dead and a child has been left an orphan. We will pursue justice for the victim's family."
Hogan said the day before the murder Twyman changed his Facebook profile picture to a shotgun shell, with a shotgun as the background.
In response to comments posted, Twyman allegedly said the picture was "a slug fool," that it was "gon be too late" if law enforcement tried to intervene, and "Once i handle my business i don't give a f***!"
"This was a premeditated and cruel murder," said Hogan. "This was not an argument, this was an execution."
Twyman was being held without bail on murder charges.
The investigation into the shooting continues. Anyone with information is asked to call East Fallowfield Police Officer Samantha Harper at (610) 384-9163 or Chester County Detective Butch Dutter at (610) 692-5100.