The mother of a battered 6-year-old Harlem boy told investigators she watched her hulking boyfriend beat her son with a wooden broomstick and hang him by his T-shirt from a hook on the bathroom door. Then she placed her dead son on a bed and rested and read the Bible.

The infuriating and sickening details of little Zymere Perkins’ final moments emerged as city investigators launched a probe Wednesday into his death — trying to determine whether a series of past child-care failures sealed his tragic fate.

The Department of Investigation demanded the documents in five previous ACS probes of abuse involving Zymere’s mom after Mayor de Blasio admitted the system he had set out to reform had failed.The child’s death Monday came two years after de Blasio vowed to reform the city’s Administration for Children’s Services and four months after a highly critical DOI assessment of the troubled agency.(nydailynews.com)…[+]