Muniz later confessed she was not assaulted, gave two other stories

A woman is charged with suffocating her fiance's daughter to death after he found racy texts on her phone and ended the relationship, a court heard.

Melinda Muniz, now 26, is charged with killing three-year-old Grace Ford on January 9, 2014 - hours after Grace's father, an Iraq War veteran, told her to move out of their Plano, Texas, apartment.

Grace, who also suffered severe injuries to her genitalia, died when she was taken off life support three days later in hospital.

This week a jury heard Muniz told police she was raped and knocked unconscious by an intruder who taped Grace's mouth shut.

However, after tests refuted her story, Muniz claimed she had amnesia and could not remember the past two years, Star Local Media reported.

Murder trial: Melinda Muniz, 26, (left) is charged with killing her fiancé's three-year-old daughter Grace (right)

In a third interview, prosecutors say, Muniz said Grace put duct tape over her mouth so Muniz panicked and knocked herself unconscious with a pan.

She then said that she noticed Grace had tape over her mouth, pulled it off, saw she was unconscious, put it back on, and knocked herself out.

She said she 'didn't know' if it was an accident or intentional, the court heard.

An investigation has since revealed Muniz was allegedly seen purchasing duct tape and zip wires hours before Grace was found lifeless on her bed with tape over her mouth and wires around the room, though Muniz claimed these were arts and crafts materials.

Searches for 'duct tape' and 'kill' were also found on a MacBook recovered from the property Muniz shared with Grace and then-fiance Mitch Ford, the jury heard.

Muniz, who acted as caretaker for Grace since father Mitch Ford won full custody in 2013, faces life in prison without parole if found guilty.

The couple met in September 2012, a year and a half after Grace was born.

He gained full custody from his ex-wife Emily Reeves Ward, who became addicted to alcohol and prescription pills after he returned from his second Iraq war and their relationship broke down.

Ford said he proposed to Muniz in December 2013 but ended the relationship on January 9, the morning after he saw she had texted pictures of her in underwear to her personal trainer.

Horrific: Grace was found face-down on the bed, lifeless, with duct tape over her mouth

Babysat: Grace, pictured with her mother Emily Ward, was being babysat by Muniz when she died

He told the court: 'As I was getting ready for work, I let her know I found that stuff on her phone,' he testified.

'It wasn't a big argument or anything. I said it wasn't going to work and called off the engagement. She was kind of unemotional, like it wasn't really a big deal.

'There wasn't a fight. I provided everything for her. I told her she had a week [to move out]. She could keep the engagement ring and sell it and keep the car to drive around and look for jobs. She didn't cry, didn't appear angry.'

The murder trial, which opened on Tuesday, has also heard evidence from the first emergency officers to reach the scene of the crime - who testified that Muniz appeared to be pretending to be unconscious.

I felt like it wasn't genuine Officer Camille Bowie who was first on the scene on January 9, 2014

'She took a big breath and kind of gently fell to the floor as if she had fainted,' Officer Camille Bowie said.

'Her eyes were kind of fluttering, like she was trying to keep them shut forcefully. There's no movement in the eyes and body when someone faints – if you really faint, you're not going to gently place yourself. I felt like it wasn't genuine.'

Ford told the court he contacted police after his phone call with Muniz was cut short.

He said he was at work, Muniz phoned to say she had just got home with Grace, and the phone seemingly fell to the floor.

He arrived at the apartment at the same time as the officers.

Muniz was lying on her front with her underwear around her ankles.

Grace was in a bedroom on her front and remained unresponsive as she was taken to ER at The Medical Center of Plano.

She was given a dose of epinephrine which started her heart, then doctors noticed bruising and blood around her vaginal area.

'I believed Grace had been sexually assaulted,' Dr Richard Honaker testified.

Stories: Muniz gave three different accounts of what happened before saying she doesn't know if Grace's death was an accident or intentional

Deborah Davis, the health practitioner who examined Muniz for evidence of sexual assault, said: 'Other than her verbalizing, I saw nothing to indicate any sexual assault. The defendant didn't seem emotional, was pretty quiet and very cooperative.'

Muniz said she had purchased duct tape, scissors, zip ties and cotton swabs from Dollar Tree for an arts and crafts project.

As she began cleaning, she said Grace must have gotten scared, thinking Muniz was about to vacuum, so she ran to her bedroom and taped her mouth.

Muniz explained that she donned gloves and partially removed the duct tape from Grace's mouth to see if she was OK.

When it was clear Grace wasn't breathing, she panicked and put the tape back on.

Then, as Grace lay unconscious, she gathered the scissors, zip ties and duct tape and disposed of it in a Dumpster across the parking lot, she said.

In a recorded interview with Muniz, played to the jury, Detective Chris Jones said: 'I'm going to be straight-up honest with you: There are issues with your story. You brought up that Grace had duct tape on her when that was never mentioned. How did you know if you were unconscious?'

He added that the time frame was unrealistic, saying the six minutes between the 911 call and authorities' arrival was 'not realistic' for an intruder to physically and sexually assault two people.