(CNN) -- Police have added a second charge of capital murder against an Irving, Texas, woman who allegedly told a 911 operator that she strangled her two young children because they were autistic, a spokeswoman for the district attorney said Friday.
Saiqa Akhter, 30, now faces two charges of capital murder of a child under 5 in the deaths of her 2-year-old daughter and 5-year-old son, Dallas County district attorney spokeswoman Jamille Bradfield said.
A woman who identified herself as Akhter called police Monday evening and said she first tried to kill her children with bathroom cleaner, but they would not drink it. She told the 911 operator that she then strangled them with a wire and that they were on her bed.
Police and paramedics tried to resuscitate the children, but Zain Akhter died at the hospital Monday, and his younger sister, Faryaal Akhter, died at the hospital Tuesday evening, according to authorities.
On the tape, the woman tells the operator, "I killed them. I killed both of them. I killed my both kids. ... They are not doing anything. They are just blue. They are not taking any breaths. Their heart is not beating."
The operator asks her what happened.
"First, I tried to give them bathroom cleaner. I put in their mouth, but they don't drink it. I want them to drink it. They don't drink it. ... I grabbed their neck ... and they are no more," she says on the tape.
The operator continues to talk to the woman to keep her on the phone until officers arrive. She asks why she killed her children, and the woman says she wanted normal children.
"They are autistic. I don't want my kids to be autistic," she is heard saying in an even tone.
The operator then asks her what she is feeling, and she says "nothing."
Akhter is being held in the Dallas County jail in lieu of $1 million bail.
According to the Texas Department of Family and Protective Services, the Akhter family had a referral in 2009 for "neglectful supervision."