HOUSTON Investigators have charged a third person with the murder of an Humble mother. She reportedly had a sexual encounter with the victim s 16-year-old daughter on the day of the killing.

Rebecca Keller, 20, now faces charges of murder and sexual assault of a child.

With this latest arrest, a young man who was charged early on in the case is proclaiming his innocence.

Zein Ahmed is out on $100,000 bond.

Police said he confessed to the murder of Mary Ann Murphy. However, he now says he had nothing to do with it.

I just told them I did it because I was scared and nervous. I was shaking, explained Zein Ahmed at his family s home.

Ahmed said he s relieved to hear of this third arrest, but police said Ahmed, the 16-year-old daughter and Keller are all equally responsible.

Somehow they put my name into it, which I don t know, said Ahmed.

Ahmed said he is a friend to Murphy s 16-year-old daughter and Rebecca Keller. His family believes police have it all wrong, and they want his name cleared.

I m sure anybody who s never been interrogated before would probably end up confessing out of being scared, said Sanam Ahmed, the suspect s sister.

Zein Ahmed said he has no knowledge of what happened on July 16th in the 8300 block of Poplar Ridge Lane. Murphy was sound asleep in her bed when police said she was brutally attacked.

The 48-year-old woman screamed as she was stabbed several times.

Police are not saying why they are just now closing in on Keller. People inside Keller s listed address did not answer when KHOU went for comment on Tuesday.

Keller s neighbors were stunned by the accusations.

She s always been so quiet, and [she] cleans the yard and everything, said neighbor Romelia Cervantes.

Neighbors said Keller did not cause any trouble in the neighborhood.

Charges is charges. Hopefully she s not involved, said neighbor Alfred Ford.

A boy who knew Murphy s daughter said things were tense between mother and daughter in the months leading up to the killing.

He said Murphy did not approve of her daughter s dating relationship with Keller.

I knew that her mom didn t like them going out, explained Carlos. I knew something was going on because her and her daughter would fight like every day or like half the days...they would come out of the garage fighting and arguing.

It s unclear if Murphy s daughter is still in custody.

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