David Matusiewicz could have asked for his freedom, but waived his right to a hearing.
He travelled with his parents to Wilmington for a child support hearing on Monday.
His father, Thomas Matusiewicz, also went with him to court and shot David's ex-wife, Christine Belford and her friend Beth Mulford.
David was immediately arrested on a probation violation. He had spent four years in jail for kidnapping his three daughters.
Lenore Matusiewicz, the children's grandmother and gunman's wife, pleaded guilty to endangering the girls' welfare and was sentenced to 18 months in prison in the kidnapping plot.
In an interview with Action News this week, Lenore Matusiewicz said she - and David - had no idea Thomas would open fire.
Earlier in the week, the government asked the court to hold David Matusiewicz indefinitely, saying he was a risk of flight and a danger to the public.
A warrant, obtained by Action News, may shed light on why. It indicates David and his father drove separate cars from Texas to a friend's house in Elkton, Maryland.
Thomas' car was found in a garage near the courthouse after the shooting. David's car was still parked in Elkton, and police found numerous firearms and ammo in the trunk.
The car was registered in South Dakota under his father's name, even though he lived in Texas.
When police searched the Matusiewicz home in Texas, another warrant said they were looking for evidence that David and his mother Lenore conspired with Thomas to commit murder.
David and Thomas hugged when they parted ways in the lobby of the courthouse.
A picture of David showed him with dark brown hair when he was arrested in 2009. However in court Friday, his hair was bleached blond.
Investigators want to know why he changed his appearance.
The next time David appears in court it will be for a hearing to revoke his supervised release.
"It's a single proceeding that with the punishment, whether it be a change of condition and imposition of an additional term of supervised release or a return to prison," said Lesley Wolfe, U.S. Attorney.
While federal officials hold David Matusiewicz in jail indefinitely, state police continue their investigation and have not yet ruled out the possibility of criminal charges against him and his mother.