Jan. 17, 2014 -- Jeannie Williams still remembers the last moment she saw her 11-year-old son Jeffrey alive.
"My last vision I have of him is just sitting on the edge of the bed and him holding the iPad and playing a game," Williams told ABC's "20/20" in an exclusive interview.
Williams and her son had checked into Room 225 at the Blue Ridge Plaza Best Western Hotel in Boone, N.C., on June 7, 2013. They were planning to pick up Williams' daughter Brianne, 17, from a nearby science camp the next day.
But during the night the 49-year-old mother felt nauseous and hurried to the bathroom. First she sat with her head between her knees, but eventually moved to the floor and laid on her side.
"I knew where I was," Williams said. "I was on the floor, but my phone was plugged in by the bed. I knew I needed to get help... I remember [being] on the floor reaching and trying to get to the door to open the door, and I couldn't. I couldn't get it. And then that's the last thing I remember."
When Williams and Jeffrey didn't arrived to pick up Brianne, she called her father, who in turn called the hotel. When a clerk went to Room 225, she found Williams and Jeffrey.
"The next thing I remember is waking up in the hospital room," Williams said. "I couldn't talk."
After she awoke, Williams scrawled a note to her husband to ask about Jeffrey, "and that's when he told me that Jeffrey was with Jesus," she said.
Williams was shocked to learn she and her son had suffered from carbon monoxide poisoning. She was even more shocked to discover that a couple had died in Room 225 just seven weeks before their stay.
Daryl Jenkins, 73, and Shirley Jenkins, 72, were found dead in the same hotel room on April 16, 2013.
On 911 tapes from the day Jeannie and Jeffrey Williams were found unconscious, a hotel employee can be heard saying, "This just happened to us last month so please come help us... You don't understand, we just went through this."
When medics arrived at the hotel they, too, realized this wasn't their first visit to Room 225.
"And I look at my partner, and I said, 'If I'm not mistaken, that's the same room we had the last call in,'" said Mike Edmisten, an EMT for Watauga Medics in Boone. "Then we walk in, and we find two more bodies, same room. Stuff like this don't happen here. That's what everybody thinks. But it does."
Damon Mallatere, the hotel manager, chose to re-open Room 225 six weeks after the Jenkins' death. Mallatere is also the president of Appalachian Hospitality Management, the company that oversees the Blue Ridge Plaza Best Western, which is an independent hotel and not owned by Best Western.
Mallatere says authorities indicated to him the Jenkins died of natural causes. The room was re-opened before Watauga County medical examiner Dr. Brent Hall determined what killed the elderly couple.
"I don't believe that anybody that was in any way involved, whether it be the authorities or the contractors or my employees or myself should go to bed tonight and not feel responsibility," Mallatare told ABC News in an exclusive interview. "[But] I would never willfully hurt a guest if I knew that I could keep that from happening."
But there was yet another blatant warning sign. Three days after the Jenkins' death, Serene Solinski hosted a birthday pool party and sleepover for her 13-year-old daughter, Levi Rawl, and her eight friends at the hotel. When they checked into Room 325, the hotel room located above Room 225, Solinski said the girls became very ill.
"All girls were very sick, puking in bathtubs, sinks, toilets while I'm calling their parents, they were falling off like flies," Solinski said. "And it was pretty scary."
According to Solinski, all but one friend went home with their parents that night, too sick to continue celebrating. She said she alerted the front desk, and "my name was written on a yellow sticky note and I was told the general manager would be told."
Mallatere denies ever being told of Solinski's stay by his staff.
After Jeffrey Williams was found dead, state investigators discovered that the hotel pool heater's exhaust pipe was damaged. In investigation photos obtained by ABC News, the pipe can be seen full of holes and propped up with a VHS cassette tape and a hotel ice bucket. Investigators say the exhaust pipe was leaking lethal levels of carbon monoxide from its location in the drop ceiling just below Room 225.
Mallatare said he had no knowledge of the damaged pipe until the state's investigation.
"We never would've re-opened that room if we had any thoughts whatsoever that there was something wrong or that that would hurt somebody," Mallatare said.
North Carolina Department of Health and Human Services (DHHS) told ABC News the medical examiner had received Shirley Jenkins' toxicology report on June 3, 2013, showing she had been killed by carbon monoxide poisoning -- four days before Jeffrey Williams died.
In a statement to ABC News, DHHS spokesperson Kevin Howell wrote, "Hall did not request that the toxicology analysis be expedited."
Hall resigned from his state-appointed post in June. He didn't respond to repeated attempts to contact him.
On Jan. 8, a North Carolina grand jury indicted Mallatare on three counts of involuntary manslaughter and aggravated assault for Jeannie Williams' injuries. After turning himself in on Feb. 10, Mallatare entered a not guilty plea and posting a bond of $40,000. He faces an arraignment hearing on Feb. 17.
Unlike smoke detectors, there is no federal requirement for carbon monoxide detectors in hotel rooms. A handful of states, now including North Carolina, do require them in some areas of the hotel.
When asked if she thought her son would still be alive if the Blue Ridge Plaza Best Western had carbon monoxide detectors installed, she said, "That's my understanding."
The Williams family hopes to start a foundation to raise awareness of the need for carbon monoxide detectors.
"One thing that we would like is for more hotels or state laws, if they would put carbon monoxide detectors in hotels," Jeannie Williams said. "If you walk into a hotel room, don't assume that everybody there is doing everything they can for your safety. As travelers, maybe we need to take more control of that for ourselves by traveling with CO detectors."
In raising awareness of the horrors she faced in Room 225, she hopes to spare another family the pain she now carries.
"One thing I'll never have… I won't have the mother and the groom dance," Williams said. "But I just take it one step at a time, and I just know I'll see him and I'll dance with him in heaven one day."