Reporter: Long after most of us put our work weeks behind us, Kelly Osborn is still up at night. Still pouring through every piece of evidence. But, by far, the most difficult pieces to study are the... See More
Reporter: Long after most of us put our work weeks behind us, Kelly Osborn is still up at night. Still pouring through every piece of evidence. But, by far, the most difficult pieces to study are the images of her dead daughter. A lot of people will ask, how could a mother look at the photographs from an autopsy? I don't recommend it to any, any parent. Reporter: But why did you? I had to. I became my daughter's investigator. I didn't have a choice. Reporter: And immediately there were clues. The kind she says only a mother would notice. The first thing I was very shocked at, looking at her eyes. Sheena and I, we wore the same mascara, and I knew that we, if you cry with this mascara on, your eyelashes are all clumped up and, and hers were perfect. Reporter: If Sheena took her own life, there were no tears. Which experts say is very rare. Her make-up, untouched. Something else only a mom would notice, that diamond bracelet they fawned over at Christmas. That is so gorgeous. Reporter: Kelly says it was on the wrong wrist. It is on her right wrist. I knew that Sheena didn't wear her bracelets on her right wrist. As a matter of fact, that video on Christmas, when she got that bracelet, she takes that bracelet out of the box, and shows it, with her right hand and automatically places it on her left wrist. Reporter: The crime scene photos also show both the bathroom and the shower doors left open. Sheena's mother convinced she would never have done that with her babies, her two little dogs right there in the room. She would have made sure that her dogs didn't see her that way. Reporter: And while that's what a mother noticed from those photos, veteran crime reporter lee Williams saw something else. There's a photo of Sheena in the shower. Her feet are caked with sand and debris yet there's no debris on the white floor, on the shower or on the white floor of the bathroom immediately outside the shower. Reporter: So her feet were caked in sand and yet there was no sand anywhere in that bathroom? None whatsoever. Other than on her feet. Reporter: For Williams, sand on her feet and not on the floor around her makes it nearly impossible to believe Sheena killed herself in that shower. So either Sheena was carried in there, post mortem, and hung or she somehow levitated into that room. Reporter: Kelly had the reporter on her side. But what she truly needed were some big names, forensic heavyweights. And she got three of them to look at all the evidence. One of them, taking "20/20" back to that very hotel room with her. Jan Johnson is one of those csi experts who examined the evidence. She's spent more than 40 years studying crime scenes and she immediately saw red flags. There was a pillow lying on the floor. I would be very interested in what's on that pillow. Reporter: Jan says a veteran investigator would have ruled everything out. Asking, could that pillow have been used to smother her? Because you're thinking someone could've used one of these pillows to kill her? Absolutely. Reporter: But most telling, says Jan, the bathroom where she says crucial evidence was missed. This is where Sheena was found hanging from a dog leash? That is correct. And it's attached to the showerhead. You can see it's clipped at the top, extending downward. The noose is around her neck, and her buttocks is about eight inches off the ground. She's extended towards the back side of the shower with her legs extended outward. Reporter: So, she's not suspended in -- in midair? No, she's not. Her legs are actually on the bottom of the shower. Flat. Yes. Reporter: Wouldn't that give someone ample opportunity to stand back up, to pull themselves back up? Absolutely. Reporter: Jan also points to her clothes. If she were convulsing after hanging herself, Jan says she would expect the clothes to be riding up the body. But the cuffs of her pants were actually down around her feet. And Jan says it looks more like she was dragged into the shower. The pants are extended outward. And you would have expected if she had, you know, walked her way down the shower wall and hung herself that the pants would've gone up her legs. I mean, her clothing is perfect. She appeared serene, like she had just fallen asleep. A hanging is a violent act. Towards the end, your body fights that. It fights the ligature. It struggles to get air. And there was no evidence of any of that. Her hair was perfectly in place. Like a mannequin that had just been pushed over on its side. I've never seen a hanging like that. Reporter: And one more giant red flag for Jan and that entire team of experts was what they saw in Sheena's eyes. So when you saw that in both eyes she had popped blood vessels, you immediately thought -- She'd been strangled. You usually see petechial hemorrhages in a strangulation. You don't often see them in a hanging. Reporter: The hemorrhaging in Sheena's eyes, they believe, is more consistent with a violent struggle. A strangling. And then the bombshell conclusion. All three experts weighing all three experts weighing in, and in every one of their reports. Three words stood out -- staged crime scene. And that's huge. That means that what was done to Sheena was staged to make it appear as a suicide. What I think happened in that room that night is, she may have been suffocated on the bed and I think that she was dragged into the shower and placed into that leash on that shower head. Reporter: Armed with those forensic experts' affidavits Kelly got a meeting with the medical examiner who had classified Sheena's death a suicide. And right there while sitting across from her, the break she was waiting for. He changed that one key line on Sheena's death certificate. They changed the manner of death to undetermined pending further investigation. We thought, well, that automatically opens this case, no. You know what detective Diaz tells me? "That's just their opinion." Reporter: In fact, that detective who answered the call remained convinced that Sheena did kill herself and he went on local station WTSP to say so. She wants to say she's not in denial. I say she is. I say she just can't accept her daughter committing suicide. Reporter: When they paint the portrait OAN obsessed mother, what do you say? It's a good thing I was. Obsessive? Or you call it just doing their job for them?
This transcript has been automatically generated and may not be 100% accurate.