Officials are investigating a Dedham house fire that killed a landlord and injured two residents on Saturday morning. The fire was reported at around 5:30 a.m. at 22 Harding Terr., where firefighters found that two residents, Andrea Moreno-Glenn and her boyfriend Moses Etheart, had made it out of the house safely.They told firefighters that Lynne O'Brien, 52, of Dedham remained trapped inside the house, according to Dedham Fire Chief William Spillane.Moreno-Glenn said O'Brien woke them up, alerting them about the fire. "As I opened the door - the smoke just came right in like whoosh."Moreno-Glenn and Etheart exited the burning home, but O'Brien did not. They said they yelled at her, but she walked back into the fire. Etheart went back into the house to find O'Brien, but he was pushed back by the fire.All Moreno-Glenn could think about was getting O'Brien out. "Please get her out. I don't care about anything else, just get her out."Firefighters entered the house and found O'Brien on the second floor of the two-story house, according to Spillane.O'Brien was taken to Norwood Hospital where she was pronounced dead, according to Spillane. Moreno-Glenn and Etheart were treated for minor injuries at local hospitals. "On behalf of the entire community, our most sincere condolences go out to the victim's family," Spillane said.Lauralee Davis, O'Brien's neighbor and close friend, found some comfort from a special pin discovered in all the debris. "It was her grandmother's, she cherished it always...and we were able to find it," she said. "It does not surprise me that she wanted them to get out first. That's the kind of person she was."Three firefighters were also treated for injuries, including a knee injury and heat exhaustion. The cause of the fire remains under investigation, but the deputy chief says the cause appears to be electrical.