A 26-year-old Colorado man has pleaded guilty to causing the death of his ex-girlfriend's toddler son after beating the child so aggressively that his intestines ruptured.

Social services had investigated reported abuse at the home just 19 days before Owen's death, after he was rushed to hospital with a broken leg while in Keel's care. Keel claimed the boy's leg got stuck in his high chair and the child was allowed to continue living with his mother, Amber Reak, and Keel.

Reak, who was in the process of obtaining a divorce from Owen's father, agreed that she wouldn't leave the child alone in Keel's care again.

But less than three weeks later, Owen suffered fatal injuries at the hands of the man, while his mother was in the shower.