Lawyers for the parents of two children killed at Sandy Hook School say one of the keys was missing from emergency folders kept in classrooms that would have allowed a teacher to lock the door on 12-14.
The request comes as part of a wrongful death lawsuit by the parents of victims Jesse Lewis and Noah Pozner against Newtown on allegations that security measures were not adequate.
The families lawyer argued that even if the teachers did not have time to lock their doors, school officials set them up to fail to be able to follow lockdown procedures. Newtown's lawyers say in court documents that a lockdown, however, wasn't ordered at any time during the shooting.
School officials had put new security measures in place at the beginning of the 2012-13 school year, including locking doors during school hours. In court documents, lawyers for Newtown said there is no evidence security was inadequate, and municipalities are immune from the liability of others.
The case is scheduled for trial in March.