Xavier Lyles was only 3 years old when he was brutally beaten to death. Medical experts determined the boy had more than 70 injuries on his little body. They said some had been inflicted months, even years, before his death.

Following a month-long October trial, a jury found the boy's mother guilty of first-degree murder, child neglect and other charges. On Monday, a D.C. Superior Court judge sentenced 28-year-old Francis Lyles to 45 years in prison.

"It's heartbreaking to think of that little boy's last hours," Judge Zoe Bush said. "He was abandoned and abused. He deserved a better life than he got. But in death, he will have justice."

Through the testimony of the family's neighbors and medical experts during the trial, prosecutors were able to present a narrative of continued physical and verbal abuse of the boy by his mother.

Assistant U.S. Attorney Cynthia Wright said it ended when Lyles grew angry with Xavier the night of June 23, 2014, and beat him before he went to bed. The next morning, she discovered his body. But before calling paramedics, Wright said, Lyles asked a cousin to come to the house.

It was then, Wright said, that Lyles began lying. She told authorities that she never struck her son and that her boyfriend had been alone with the boy and had beaten him. At the time, Lyles, her three children and the boyfriend shared the apartment in Southeast Washington.

For months, police suspected the boyfriend and investigated him as the primary suspect. Some of Lyles's family members threatened the man on social media, encouraging street vengeance against him, Wright said.

Lyles's family members were outraged and wanted to help secure the arrest of Lyles's boyfriend. One of Lyles's cousins told police she had recorded conversations on her cellphone with a recording app and gave prosecutors permission to access them.

The recordings, however, did not implicate Lyles's boyfriend, prosecutors said. Instead, prosecutors say that Lyles can be heard describing harming the child after he knocked over his newborn brother's bouncy seat while the infant was in it. On the recording, Lyles, using the child's nickname, said she "f---ed Xay up."

Lyles's boyfriend was not arrested in Xavier's death and later testified during Lyles's trial that she often abused the boy.

In addition, a neighbor testified that she once found Xavier wandering outside in the cold without a coat or shoes and that when she returned the boy to his mother, she overheard Lyles beating him.

"There was a pattern of neglect and abuse," Wright told the judge. "After beating him, she left that little boy to die alone. She left that little boy alone for 15 hours to die alone."

Lyles's attorney Elliott Queen said his client maintains she did not hit Xavier or cause his death. He also said that, other than Lyles's ex-boyfriend, no one testified to seeing his client hit her children.

Queen also said that Lyles had a "troubled" childhood and that she had tested as having a low IQ. Queen did not elaborate on either statement.

Wright made the unusual request of asking the judge to sentence Lyles to life in prison. "This was an extraordinary case," she said. "Her actions were unreasonable, cruel, beyond the pale and atrocious."

Lyles did not testify during the trial. At her sentencing, she tearfully said she was not responsible for Xavier's death.

"I would never hurt my kids. I loved them more than life itself," she said. "My son is gone. I would never hurt my kids. I loved them too much."

As part of the sentence, the judge required Lyles to undergo an anger management program, grief counseling and drug treatment.

Lyles still faces additional charges in the case. Prosecutors say Lyles tried to tamper with witnesses who were scheduled to testify during her trial. A hearing for that charge — should prosecutors decide to move forward with the case — is scheduled for March.