Two months after her boyfriend was convicted of manslaughter in a trial that increased suspicions about her, Jessica Caldwell went on trial in St. Paul on Thursday for the 2009 death of her 2-year-old son.

Prosecutor Karen Kugler outlined in opening arguments before a Ramsey County District Court jury how Caldwell had been in bed with the boy throughout a night during which prosecutors say he suffered a "brutal beating."

At first, Caldwell balked at taking Julian James-Robert Williams to a hospital when he complained of pain, Kugler said. Later, after the toddler died, she laughed throughout an interview with police and "never asked them to find the murderer," Kugler said.

But Caldwell's attorney, Ira Whitlock, said the 24-year-old was nothing but "the good mother." He also raised the possibility that Caldwell's brother may have had a hand in the boy's death.

He said that no one ever saw Caldwell abuse Julian during his short life. She was the one who called 911 when her boyfriend, Demetrius Willis, 23, alerted her to the limp baby, Whitlock said. If she lacked emotion when speaking with police, he said, it was because she was raised to be tough.

As Caldwell sat, dressed in a gray pinstripe suit and bearing a tattoo dedicated to her son, Whitlock stood behind her and said: "This is a young lady who had nothing to do with the death of her son."

Caldwell and Willis were charged with identical counts of unintentional second-degree murder, first-degree manslaughter and second-degree manslaughter -- seven counts total for each. In September, a jury acquitted Willis of six counts but convicted him of the second-degree manslaughter charge for failing to get help for the toddler after he was injured. One of his attorneys said then that "it seems like the jury realizes Jessica was the main actor."

Julian died on Sept. 10, 2009, after being found not breathing and without a pulse at Willis' house at 833 York Av. in St. Paul. A medical examiner testified at Willis' trial that the toddler's pancreas had been split in half, his liver lacerated and his abdomen, arms, back, face and legs bruised. He died of complications of blunt force chest and abdominal trauma, the medical examiner said.

Prosecutors contend that Caldwell and Willis were the only people with the boy overnight when the assault occurred. He was found in grave condition about 5 a.m., yet about eight hours earlier, he laughed and played on a Metro Transit bus headed to Willis' house, bus video footage showed.

Throughout the earlier trial, and again during opening statements Thursday, prosecutors offered no explanation as to how the injuries occurred. On Thursday, Kugler focused on the timing of his emergency care at Children's Hospital and a physician's opinion of when the damage -- likened to the impact of a car accident -- may have been inflicted. By Kugler's estimate, the assault occurred after midnight, or about the time Caldwell was in bed with him, she said.

Kugler, too, referenced the incident between Julian and Caldwell's brother, which took place the previous day. She said that the brother tapped the boy on the butt after the toddler bit him. Nothing unusual, she said.

Whitlock never explicitly accused the brother of causing the boy's death. But he noted that Caldwell's brother had a cast on his hand at the time and that a doctor was prepared to testify that a cast can be used "as a weapon."

Of the brother's claim that he had merely tapped the boy, Whitlock told jury members: "You'll have to decide if that is credible."

Caldwell's trial is expected to continue into next week.

Willis is scheduled to be sentenced on Jan. 4.

Anthony Lonetree • 612-875-0041