NEWTOWN, Conn. -- A bomb scare at a church jangled the nerves of this grieving town Sunday as people were struggling to deal with the aftermath of the second-deadliest school shooting in U.S. history.

Police still aren't saying why Adam Lanza, 20, forced his way into Sandy Hooks Elementary School on Friday, then swiftly and methodically killed 20 young children and six adults. And though authorities said they have seized substantial evidence so far, they hinted Sunday that the investigation could take weeks.

"We have everything and everybody focusing on this case," said Lt. Paul Vance of the Connecticut State Police, which has more than 250 officers working the investigation. "Our goal is to paint a complete picture so that we all know and the public knows exactly what happened here."

Vance was able to shed some new light on Friday's tragic events. Though Lanza gunned down all 26 victims using a Bushmaster AR-15-style rifle, he took his own life with a handgun.

He still had hundreds of rounds of ammo in the form of several unused high-capacity magazines, even after firing dozens of bullets.

The state medical examiner was able to confirm Adam Lanza's mother, 52-year-old Nancy Lanza, was the first victim at the home she shared with her son.

Without a motive, residents are at a loss to make sense of the tragedy.

"Suicide is bad enough," said Lee Clifford, a resident of nearby Oxford who attended Sandy Hooks. "When he left his house, he knew he wasn't coming home. Why did he have to take these kids with him?"

Those attempting to mourn were further rocked when St. Rose of Lima Catholic Church was forced to evacuate after an anonymous caller threatened to trigger a bomb during Mass.

The church -- which will hold funerals for eight of the child victims later this week -- closed for the day, after remaining open since Friday.

"Sick people," said Newtown resident Steve Cross after evacuating. "We'll have to deal with this for a while. But in time, it will dissipate."

Throughout the cold, misty day, residents of Newtown stopped by a makeshift memorial underneath a town Christmas tree not far from the school. Stuffed animals, candles and flowers were placed at the foot of the tree as families cried and held each other.

Zachary Freedman, 9, and Madison Freedman, 8, put homemade pictures of a rainbow and an angel under the tree. In child's handwriting, the words "May God protect you" were scribbled on one of the drawings.

"We moved here from Massachusetts to be in a safe, quiet community," said their father, David Freedman. "It makes you feel like nothing is safe anymore."