Police have detained a California man who was exchanging messages with the teenage girl who committed a mass shooting at private Christian school in Madison on Monday.
The DIY weapons, which lack serial numbers and are attainable without transfer records or background checks, are at the center of next week's major gun debate.
A reward of up to $100,000 is being offered by the FBI and Crime Stoppers for any information that leads to the arrest and conviction of the persons responsible.
Attorney General Loretta Lynch has defended President Barack Obama's say on restriction of gun laws, saying that his steps were legal.
