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First Posted: 10/09/12 04:16 PM ET EDT Updated: 10/10/12 11:00 AM ET EDT

HOUSTON -- Police say a Southeast Texas woman who is pregnant with her fourth child has been charged in the deaths of her two infant sons.

Kristi-An Walker remained jailed Tuesday on murder and two other charges relating to the deaths that occurred separately. One was in April 2011 and the second was in June.

Angleton police say the 20-year-old mother told investigators she became frustrated with the boys because they wouldn't stop crying.

Court records did not list an attorney for Walker.

Police Sgt. Kirk Coleman says authorities began investigating Walker after her 6-month old son died June 21. Police say the probe led investigators to the 2011 death of her 4-month-old son. Police say both boys died from head trauma.

Walker's 3-year-old son is in foster care.