San Bernardino school had no knowledge of teacher's troubled relationship with shooter, police say The new information helps explain why the shooter was allowed into the school.

 -- California school officials at the site of Monday’s killing and suicide that left three people dead had no prior knowledge of the ongoing conflict between slain teacher Karen Smith and the estranged husband who shot her and two students, according to police.

Interviews indicate that Smith was somewhat private about her personal life and shared details only with her immediate family members, police said, which would suggest why North Park Elementary School in San Bernardino allowed Cedric Anderson to visit her classroom without suspicion when he said he had something to drop off for her.

When access was granted, Anderson of Riverside, California, walked into the special-needs classroom and opened fire on Smith, "without saying anything," before turning the gun on himself, San Bernardino Police Chief Jarrod Burguan said Monday.

The teacher’s daughter also confirmed to investigators that Smith never took his threats of violence seriously and that there was never any sense of danger in her relationship with Anderson, police said.

The victims of the attack

Anderson and Smith, both 53, were found dead in the classroom after the incident, which occurred at around 10:30 a.m. local time, Burguan said. There were 15 students and two aides in the mixed special needs classroom at the time.

Two male students, who were injured as Anderson fired at his wife, were taken to a hospital for treatment, police said.

One of them, 8-year-old Jonathan Martinez, died later from his injuries after being airlifted to Loma Linda University Medical Center, Burguan said. Martinez had Williams Syndrome, a developmental disorder that affects many parts of the body, said San Bernardino Unified School District Superintendent Dale Marsden.

The other student, a 9-year-old, is hospitalized in stable condition, Marsden said. He sustained a single gunshot wound to his upper body, Burguan said, declining to further discuss the boy's condition other than that he is improving. He is currently awake and was watching cartoons while being interviewed by authorities, Marsden said.

Smith had been working for the school district for 10 years and began working at North Park Elementary School in 2015. Her four adult children have been accounted for, Burguan said.

The gunman's history

The shooter had a criminal history that included weapons charges, drug charges and accusations of domestic violence, Burguan said. He had been arrested four times from 1982 to 2013, but was never convicted of any of those charges, Burguan said.

In the past, Anderson had served as a pastor at a church in the Los Angeles area, Burguan said, but most recently worked as a maintenance worker. At the time of the shooting, he added, he was unemployed and trying to start his own business.

Police said Anderson used a Smith & Wesson .357 revolver, firing 10 rounds and reloading once during the attack. The gun was originally purchased in 1979 in Michigan, Burguan said, but Smith was not the buyer. He added that police are still investigating the remainder of the gun's history.

Anderson has four adult children, all of whom have been accounted for, Burguan said.

How the gunman gained access

External closed-circuit TV shows Anderson tried to gain access through a secondary door but it was locked, per protocol, so he had to enter through the main entrance, police said.

Anderson was a "known person" by school staff, and all the precautionary procedures were taken to confirm his identity when he arrived at the school, Marsden said.

Capt. Ron Maass, who is leading the investigation for the San Bernardino Police Department, said the shooter entered the building on a visitor’s pass and signed in at the front office.

Anderson had told school personnel he was there to drop something off to his wife, which is "not uncommon," according to Burguan. There is no indication that the gun was visible upon the suspect's arrival to the school, Maass said.

The gunman had walked a "short distance" into the classroom before he began to open fire, Burguan said. Anderson was toward the middle of the room, about 10 to 15 feet away from the door, and the two students were very close to Smith, Burguan said.

There was "no reason to believe" the students were specifically targeted in the shooting, Burguan said, adding that he did not know why Anderson chose to kill her at the school.

"No one has come forward to say they saw this coming," Burguan said Monday afternoon during a news conference.

The gunman's relationship with his estranged wife

The gunman’s "relatively short" marriage and his alleged history of crime and drug use preceded the attack at the grade school, according to police.

The couple had been together for years, but were only married from January to March, Burguan said. They separated in March after some marital problems and Smith moved out of their home, Burguan said. She had been staying with family, including her adult children.

Smith's family told investigators that there were allegations of infidelity in the relationship, but the claim has not been verified, Burguan said. He added that Anderson apparently had contacted his wife to convince her to come home.

Smith was "resistant to that," Burguan said.

Those "closest to Smith" said she expressed concern about his "odd behavior," Burguan said. Anderson had made threats toward Smith, but those did not appear to include shooting threats, Burguan said.

Smith did not take Anderson's threats seriously and "thought he was making them for attention," Burguan said.

Note found at the gunman's home

While searching Anderson's residence, police did not find a suicide note, but did find a note he appears to have written about needing closure and feeling disrespected, Burguan said Tuesday. The note also mentioned "fixing things," he added.

Had police found the note outside of these circumstances, they wouldn't have reason to believe it was a suicide note, Burguan said. The note has not been confirmed at this time to be Anderson's.

Community reaction

Residents in the neighborhood held a candlelight vigil outside of the school Monday evening.

Students, close in age to the special education students who were shot in the attack, told ABC Los Angeles station KABC-TV that Smith was a "good teacher."

One girl described Smith as a "nice" teacher who would "help people that needed help."

The community also hosted a prayer vigil at Our Lady of the Assumption Church in San Bernardino Monday evening.

"Sometimes all we can do is cry. And today is the day for that," Bishop Gerald Barnes said at the gathering. "We'll get up again. We'll move on. We'll become stronger. But today is the day to cry."

North Park Elementary School will be closed until Monday, Marsden said.

ABC News' Alex Stone and Josh Margolin contributed to this story. Reporting from The Associated Press is also included.