Police have identified the gunman as 68-year-old Thomas Matusiewicz of Edcouch, Texas.
Police sources say Matusiewicz's intended target was one of the victims, 39-year-old Christine Belford, the ex-wife of Matusiewicz's son, David.
Belford and her friend, 47-year-old Laura Elizabeth Mulford of Newark, were both killed in the attack.
Investigators say both Thomas and David Matusiewicz were at the courthouse at about 7:40 a.m. Monday. David, who was there for a child support hearing involving Belford, had already gone through the security station.
Police say Thomas Matusiewicz never breached the security perimeter beyond the metal detectors inside the courthouse.
At about 8:15 a.m., Belford and Mulford entered the public lobby. Police say Thomas Matusiewicz approached and shot Belford. Mulford was shot as she tried to flee.
Capitol police officers exchanged fire with Matusiewicz. Both officers were hit in their bulletproof vests and were not seriously injured.
Police say Matusiewicz was wounded during the gunfire, but then shot himself in the head. His death has been ruled a suicide.
His sister-in-law says 68-year-old Thomas Matusiewitcz had become very quiet and was acting worried over the past week.
"We've been worried about Tom's thought process for a long, long time because it came to light he has a tumor," M'Linda Kula said.
Police confirmed that the shooting is related to an ongoing child custody dispute case that has been played out in Delaware courts for years.
David Matusiewicz was convicted in 2009 of kidnapping their three children and taking them on a 19-month odyssey across South America. He was later caught and sentenced to four years in prison.
Thomas and David Matusiewicz had been living in Texas and recently drove up to Delaware for court.
David Matusiewic was located by police at the courthouse and is now being held on a probation violation.
He was arraigned on those charges Tuesday afternoon.
He never made eye contact with his mother, Lenore Matusiewicz, who sat in the back of the courtroom.
Lenore Matusiewicz kept her thoughts to herself as she left the courthouse.
The government says her son David violated his probation by not staying with her at her brother's house in Ocean County, New Jersey.
Instead, he spent Sunday night at a home in Elkton, Maryland.
The government says he lied to his probation officer about where he was staying.
His mother has also now been ordered by a judge to stay at least 1,000 feet away from her grandchildren at all times and can have no direct or indirect contact with them.
The state argued she is a danger to them.
The state is also arguing that David Matusiewicz is a danger to the public and a flight risk. He is being held without bail until a detention hearing on Friday.
The courthouse remained closed Tuesday as the investigation continued.
Belford leaves behind four children. Mulford, a wife and mother of two, had come to the courthouse to support her friend.
WORKERS, JURORS WITNESSED THE HORROR
People who were inside the courthouse when the gunfire erupted described a terrifying scene.
It was the beginning of the work week and people were filing in - both workers and people who were reporting for jury duty. They were going through security when the shots rang out.
At first it wasn't clear whether the shots were coming from a lone gunman or if something else was going on. People were quickly moved to safe areas, and they remained there until an all-clear was given.
"I saw the guy come through the door and point-blank shoot two women," said juror Chick Chinski. "In fact, I didn't realize it was gunfire at first. Then when I saw a cop hit the floor, I hit the floor, and everyone else was going down at that point. There were maybe 50, 60 people in the lobby."
It had been a routine, rainy Monday morning. Then literally in a flash it became a terrifying ordeal inside the New Castle County Courthouse.
"We heard the gunfire," said courthouse employee Wanda Dean. "Some security staff came in and told us to stay in the office, stay down, there was a shooter outside. And one of our security staff was brought in. He had evidently been hit by debris from the broken glass."
"Yes, you do go through panic and terror. Like, okay this can't be happening in a courthouse," said juror Greg Simpson. "But yes, it's happening at the courthouse."
For hours the big courthouse was effectively locked down. Employees were released room by room and then told similar stories.
"There were a lot of people crying, people who actually saw the whole scene," said another witness. "They were just traumatized and shaken up."
"It was such a harrowing experience," said courthouse employee Beverly Bridgeforth. "I've never experienced anything like this before. I've been here ever since this courthouse has been here."
BELFORD'S NEIGHBORS STUNNED
Residents in Christine Belford's Middletown, Delaware neighborhood were stunned by the news that the mother of four was presumed dead in the courthouse shooting.
"Nobody ever thought something like this would happen," neighbor Tracy Campbell told Action News.
In a Facebook post shared only with Action News, someone posting as Christine's daughter confirmed her mother passed away Monday morning.
"She would go to the ends of the earth for her kids," said former co-worker Janet Jilek. "Her kids were her life. There was nobody who was more important to her than her kids."
Friends confirm Belford was in an ongoing custody battle with her ex-husband David Matusiewicz.
"She was terrified of him," said another neighbor who only wanted to be identified as Lois. "When she moved into that house she had all the windows wired, she had cameras outside."
"She said, 'But he does owe us money, and he doesn't want to pay it so he's coming to fight it,'" said Lois. "The courts didn't protect her like they needed to. She asked for help, and they let her down."
MULFORD'S FAMILY RELEASES STATEMENT
From the family of Laura Elizabeth Mulford
Our hearts are full of sorrow today with the loss of our wife and mother Beth Mulford Beth was tragically taken from us in the senseless crime at the Newcastle Court house yesterday. Beth was a loving wife to John and beloved mother of Christina and Katlyn. A registered nurse, Beth worked locally as an emergency room nurse, in the pharmaceutical industry and as a school nurse. Beth was a friend to many her kind heart and generous spirit were evident in her support for her friend Christine.
Beth was a blessing to those who knew her. She will be deeply missed by her family and many friends.