Josh Powell with sons Charlie and Braden
Amber Hardman/Hardman Photography/Polaris
02/09/2012 at 05:00 PM EST
Social worker Elizabeth Griffin Hall, who was present when Josh Powell blew up his home
with his two young sons inside, is now revealing chilling details of their final moments.
When Hall arrived at Powell's home for a supervised visited with Charlie, 7, and Braden, 5, he managed to get the boys inside but immediately shut Hall out.
"He caught my eye, his shoulders were slumped. He had a sheepish look," Hall tells ABC's 20/20
in an interview set to air Friday. "He just shrugged his shoulders and slammed the door."
Hall says that after Powell had his sons alone inside the house, "I heard him say, 'Charlie, I've got a big surprise for you.' ... And then I heard Braden cry out."
According to authorities, Powell used a hatchet
on his sons' heads and necks before blowing up the house and killing himself and his sons.
Hall says she called out to Powell – who was a person of interest in the disappearance of his wife Susan Powell and had since lost custody of his sons – to open the door, but became suspicious when she smelled gas.
"I'm saying, 'Let me in, Josh, let me in,' " Hall said. "I realized I didn't have my phone in my hand and I could smell gas. Too much time had passed and I could smell gas."
Though she sensed that something was very wrong, Hall could not get into the house. "I wanted to get to the kids. I would have broken in if I could," she tells 20/20
Though Hall says Charlie and Braden loved spending time with their father, she now believes that "Josh Powell was really, really evil."
Hall describes her fondness for Powell's sons and shares memories of her time with them. Braden was "a free spirit" who "smiled all the time" and Charlie "was smart and funny," says Hall. "He loved bugs and frogs."
Though the experience was traumatizing to Hall, she won't quit being a social worker, a job she adores.
"God called me to do this," she says. "I am not going to be [Josh Powell's] victim. He's not going to destroy my passion for children. He's not going to stop me from working with children."