SAN BERNARDINO (CBSLA.com) – A teacher’s assistant who witnessed a murder-suicide in a San Bernardino school classroom earlier this week described the harrowing experience Thursday.

Jennifer Downing was in a North Park Elementary School classroom Monday morning when the estranged husband of her co-worker, Karen Smith, entered and opened fire on his wife. Downing said had she been armed, it would not have helped.

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“There was absolutely no reaction time, because it was right away,” Downing said. “There wasn’t, ‘oh maybe I should grab something or get something.’ Had something (a gun) been locked up, it would not have mattered.”

FULL COVERAGE: San Bernardino School Shooting | Photos

San Bernardino police said Cedric Anderson, 53, entered his wife’s special-needs classroom and shot her dead. Two students standing behind her at the time were also struck by gunfire. Eight-year-old Jonathan Martinez was killed. Nine-year-old Nolan Brandy was critically hurt, but survived. Downing got a chance to visit Brandy in the hospital.

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“It was a joyful experience,” Downing said. “He was a bit shy, which was to be expect, but a lot of happiness.”

For the first time since the shooting, staff returned to the campus Thursday.

“And we all walked the halls together as a tight unit, and I was OK,” Downing said.

Classes will resume at the school Monday.

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A GoFundMe page has sent set up to assist with medical expenses for Brandy’s recovery. To donate, click here.