NEWTOWN, Conn. (AP) -- A group in Newtown is launching a grassroots initiative in response to last month's school shooting to prevent similar tragedies.

Sandy Hook Promise, formerly known as Newtown United, plans to announce the initiative Monday.

The group said Friday it invited victim family members to the event. A co-founder of the group, Tim Makris, said he doesn't have a count of how many families might participate. He said the families are at varying stages of grief and recovery, and some may never want to discuss the issues.

A gunman shot his way into Sandy Hook Elementary School on Dec. 14 and killed 20 first-graders and six women before committing suicide as police arrived. He also killed his mother before driving to the school and carrying out the massacre.