ANGLETON, Texas, Oct. 10 (UPI) -- A Texas mother accused of fatally beating her 6-month-old son has told investigators it wasn't the first time she killed a baby, police said.

Sgt. Kirk Coleman of the Angleton, Texas Police Department said Kristi-An Walker, 20, faces several charges, including homicide, after she confessed to beating the 6-month-old baby, KSEE-TV, Houston, reported.

Coleman said Walker later told investigators that in April 2011 she killed a 4-month-old son.

"She claims on both occasions she would throw the kids up against the wall," Coleman said. "She was irritated with the crying and all that stuff."

Walker has been charged with murder and two counts of felony injury to a child. If convicted, she faces up to 99 years in prison.

Investigators said Walker is pregnant.