TULSA, Oklahoma - The mother of a murdered baby took the stand on Monday to testify against her ex-husband.

The former TU student is accused in the shaking death of his six-week-old son.

Luna Lu told jurors she never had concerns for her baby’s safety around her ex-husband, Sebastian Aguirre, but she admitted Aguirre was growing frustrated with how much their son cried in the weeks leading up to his death.

Aguirre is charged with child abuse murder in the death of his six-week-old son, Etienne.

Lu told the jury she found out she was pregnant with baby Etienne a week after she ended her relationship with Aguirre.

She testified she found out Aguirre was having an affair with another woman, but that they agreed to get married when they decided to keep the baby.

Lu said Aguirre was excited about the baby and had hopes and dreams for the child’s future.

She said that over time, however, Aguirre grew frustrated with how much Etienne cried and that he would sometimes put a washcloth in the baby’s mouth or press the baby’s mouth against his own cheek to quiet him.

Lu said they had a big fight just days before Etienne’s death when she learned Aguirre was still having an affair with the same woman.

However, Lu testified she didn’t know if it was in Aguirre’s nature to do something like this and that she feels like, to this day, she doesn’t know exactly what happened to her son.

Aguirre’s attorneys are just now starting to present their case.  There’s no word yet on whether Aguirre will testify in his own defense.