It happened inside the Wawa on Sugartown Road in Radnor Township on Thursday night.
Police tracked him down to Thornbury Park in Glen Mills.
Kennedy, 34, was in his BMW and, in the trunk of his car, was an AR-15 assault-style rifle.
Delaware County DA Kat Copeland said, "With an AR-15 he brutally murdered the mother of his child. In a public place in cold blood, placing numerous others at risk."
The criminal complaint states detectives watched video of Kennedy pulling up to the Wawa in his BMW.
Then he went to retrieve a rifle from the trunk.
Next, Kennedy is seen leaving the Wawa carrying the rifle.
The complaint also states while he was inside four Wawa employees witnessed the shooting. Some of them even recognized Kennedy as a repeat customer.
Copeland said, "This is a classic case of what can happen in situations regarding domestic abuse and violence with the use of firearms."
After the crime, police say, Kennedy got in his car and drove to the park.
But when he was found police had him taken to a local hospital.
We asked investigators if he tried to kill himself.
Christopher Flanagan, Superintendent is the Radnor Township Police, said, "We don't know at this time. We haven't been able to talk to him or interview him."
Investigators also said it's possible Kennedy had this planned. The Wawa may have been the location for a custody exchange of their child.
We also found out this isn't the first case of domestic violence between them.
The DA says Miller had a previous protection from abuse order placed against Kennedy but there's only so much that can do.
She said, "If someone wants to get a gun legally or illegally unfortunately that's always going to be an option for them."
Kennedy has been charged with numerous crimes including criminal homicide.
Their child was not present at the time of the shooting.
Friday night, the victim's family gathered at a home in Devon while police searched the suspect's apartment.
"I presume some mental disorder there must be. There's no other logical explanation," said Colin Broom of Villanova.
Nick Smith, of Wayne, says, "It goes to show the larger issue we have in this country. That's the type of weapon that was used in the crime seems to be consistent with the types of weapon used in a lot of crimes."