(CNN) -- A Texas couple charged with killing the little girl known as "Baby Grace" now face capital murder charges, after a Texas grand jury upgraded the charges on Wednesday.



Riley Ann Sawyers was moved from Ohio to Texas by her mother.



Prosecutors said they have not decided whether to seek the death penalty against the girl's mother, Kimberly Dawn Trenor, and Trenor's husband, Royce Clyde Zeigler II.



Two-year-old Riley Ann Sawyers was beaten to death and her body was disposed of in Galveston Bay.



Riley's body was found October 29 by a fisherman on an uninhabited island in the bay. It was wrapped in black plastic bags and stuffed in a blue, plastic bin.



Her identity was not known at first, and police dubbed her "Baby Grace." Police sketches of the child were widely distributed, and Sheryl Sawyers, the girl's paternal grandmother, contacted police from her Ohio home to say the drawing resembled her granddaughter. DNA testing confirmed the child's identity.



Trenor, 19, and Zeigler, 24, were initially charged with injury to a child and tampering with evidence.



But since the initial charges were filed last month the investigation has continued and police have gathered additional evidence, in addition to confirming Riley's identity, said a statement released Wednesday by Galveston County Criminal District Attorney Kurt Sistrunk.



Based on that, the grand jury was asked to upgrade the charges, he said. A three-hour hearing was held Wednesday in which grand jurors heard testimony from five witnesses, including police and FBI investigators and the medical examiner.



The grand jury deliberated for only three minutes Wednesday before upgrading the charges, Sistrunk said.



Trenor told police Riley had been beaten and thrown across a room and that her head was held under water before she died July 24.



She said the couple hid the girl's body in a storage shed for one to two months before putting it in the plastic container and dumping it into the bay.



A medical examiner said Riley's skull was fractured in three places that would have been fatal injuries.



Trenor and the girl moved to Texas from Ohio in May to be with Zeigler, who Trenor had met online.



Sistrunk said the investigation is continuing, and a decision on whether to seek the death penalty will not be made until its conclusion. E-mail to a friend
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