Adam Lanza fought with four teachers at Sandy Hook Elementary School the day before massacre

Reports have emerged that Adam Lanza had visited Sandy Hook Elementary the day before Friday’s massacre during which he was involved in an altercation with four teachers – three of whom are now dead.

The fourth teacher – and only survivor of the altercation – wasn’t at school on Friday and is currently being interviewed by investigators. It hasn’t been revealed what the argument was over or if it was reported to authorities.

The staff member’s testimony might be an “important piece of information” for discerning motive in this case, reports NBC.

While initial reports had suggested school principal Dawn Hochsprung buzzed Adam Lanza into the building – bypassing the newly-installed security system – police have confirmed that the shooter forced his way in.

Adam Lanza opened fire on Friday morning at Sandy Hook Elementary School, which teaches children aged 5 to 10. He murdered 26 people at the school before turning the gun on himself, as well as killing one other person – his mother – at another nearby site.

Investigators said they have found “some very good evidence” to explain what drove gunman Adam Lanza, 20, to slaughter 20 children, including Ana Marquez-Greene and Jesse Lewis, and six adults at the Connecticut elementary school.

“Our investigators at the crime scene … did produce some very good evidence in this investigation that our investigators will be able to use in, hopefully, painting the complete picture as to how – and more importantly why – this occurred,” Connecticut State Police Lieutenant Paul Vance told a news conference Saturday morning.

“We’re hopeful it will paint a complete picture,” he said.

All the bodies were removed from the school overnight and a medical examiner is expected to release the names of the victims on Saturday.

Police have assigned a trooper to support each victim’s family in the days ahead. Paul Vance asked reporters to respect the families’ grief and privacy.

“This is an extremely heartbreaking thing for them to endure,” said Paul Vance.

It is expected that investigators will take another two days to process the school crime scene where it is believed Adam Lanza fired as many as 100 rounds from his guns.

“It’s going to be a slow, painstaking process,” said Paul Vance.

The adult woman found at the secondary crime scene is believed to be the shooter’s mother, Nancy Lanza.

Nancy Lanza legally owned a Sig Sauer and a Glock, both handguns of models commonly used by police, and a military-style Bushmaster .223 M4 carbine, according to law enforcement officials who also believe Adam Lanza used at least some of those weapons.

Nancy Lanza was an avid gun collector who once showed him a “really nice, high-end rifle” that she had purchased, said Dan Holmes, owner of a landscaping business who recently decorated her yard with Christmas garlands and lights.

“She said she would often go target shooting with her kids.”

Grief-stricken members of the community tied white balloons to the sign for Sandy Hook school today in honor of all those who lost their lives.

Outside Saint Rose of Lima Roman Catholic Church in Newtown, Connecticut, mourners left teddy bears, flowers and lit candles for victims.

Newtown was ranked the fifth safest city in America by the website NeighborhoodScout.com based on 2011 crime statistics.

“This wonderful town that we all love for its peace, beauty, the great schools – all of that – has become Columbine,” said Julie Maxwell Shull, a sixth-grade teacher at Reed Intermediate School, referring to the high school that was site of a 1999 shooting in Colorado.

Many people who live in the wealthy, wooded town commute to New York City, about 80 miles away.