PROVIDENCE, R.I. — A man who struck his girlfriend's 3-year-old nephew and caused the child to fall down a staircase was convicted Thursday of second-degree murder.

Gilbert Delestre, 27, also was convicted of conspiracy to commit murder in the death of Thomas "T.J." Wright. He faces a maximum sentence of life in prison plus 10 years.

Prosecutors said he and his girlfriend, 25-year-old Katherine Bunnell, took turns beating T.J. in October 2004, after returning home from a night out drinking and finding a mess of food and feces in their apartment in Woonsocket.

The boy died the next day of brain injuries after being pulled off life support.

Delestre testified that he had hit T.J. on the head, causing the child to flip backward down a staircase and lose consciousness. But he said he did not intend to kill the boy and had asked jurors to convict him of manslaughter instead of murder.

Delestre's attorney, Robert Mann, said he was relieved Delestre was acquitted of first-degree murder. Delestre and his attorney have not decided whether to appeal.

"He has been devastated," Mann said. "He is very remorseful."

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Patrick Lynch, the state's attorney general, said in a statement that he was disappointed by the verdict because it "does not adequately address the depth of his involvement or the darkness of his crime."

Bunnell was convicted of second-degree murder in May and sentenced to life in prison with the possibility of parole in less than 25 years.

Thomas and his two older brothers were placed with the couple while their mother was in prison out of state. A state panel that investigated the death concluded the state never should have placed the boys with Bunnell and Delestre, who each had juvenile records, were unemployed and were raising two of their own children.

But the state Department of Children, Youth and Families had determined the couple were suitable guardians and was processing their license as foster parents when T.J. died.

The case sparked a review of Rhode Island's foster care system. The governor replaced the director of the children welfare department after the boy's death.

(This version CORRECTS Delestre's maximum sentence to life plus 10 years.))