"We don't have any smoking gun to say this is why it occurred, at least not yet," said J. Paul Vance, a Connecticut State Police spokesman. "We are moving forward and working with our partners, and as you can assume with multiple deaths, we are looking at several months before we really have our arms wrapped around this."
Attorney General Eric Holder Jr. traveled to Newtown on Thursday to meet with first responders and law enforcement officials. Officials declined to characterize the nature of the meetings.
Holder's visit comes as the Obama administration frames its response to the Dec. 14 shootings, including pushing for new gun-control measures next year.
Before visiting Newtown, Holder attended a meeting with Vice President Joe Biden and other senior administration officials to begin developing proposals that Obama plans to submit to Congress as early as next month.
"The president is absolutely committed to keeping his promise that we will act," said Biden, who is heading the working group. He said that Obama will push for a ban on assault weapons and added, "We have to have a comprehensive way in which to respond to the mass murder of our children that we saw in Connecticut."
House Speaker John Boehner, R-Ohio, promised Thursday to "take under advisement" any suggestions to curb gun violence put forward by the Biden commission.
"When the vice president's recommendations come forward, we'll certainly take them into consideration," Boehner told reporters. "At this point, our hearts and souls ought to be thinking about those victims" of the school shooting.
Holder visited Newtown on the same day that funerals caused gridlock on city streets. With hundreds of mourners arriving for viewings, local officials have said that managing the funerals is their top priority.