05/09/2012 06:47 pm ET Updated May 10, 2012

Donte Johnson Convicted Of Sabina O'Donnell's Murder, Sentenced To Life

A 20-year-old man described as having the mind of an 11-year-old was sentenced to life in prison for the rape and murder of a Philadelphia waitress.

A jury deliberated for less than four hours before convicting Donte Johnson today for the 2010 killing of Sabina O’Donnell.

Johnson admitted to the attack, telling police that he intended only to steal her bicycle, CBS Philly reported. He said he killed her, because she screamed when he tried to get her bike.

Later, he recanted his confession, which his attorneys said he made because he was mentally challenged.

Johnson maintained his innocence today during sentencing.

How can you clearly say I did anything?” Johnson said when Judge Glenn Bronson announced a sentence of life plus 40 to 80 years for first-degree murder and four other felonies.

“If I did something, I would take responsibility," Johnson said.

The prosecution relied on DNA evidence and video surveillance, according to TV station WPV, to convince jurors that Johnson beat and dragged O'Donnell to a vacant lot behind her apartment building where he raped and strangled her.

Sperm found at the crime scene allegedly matched Johnson's genetic makeup.

"My heart continues to go out to Sabina's family and friends," said District Attorney Seth Williams in a statement. "I hope this verdict will give them some sense of justice."

Johnson's attorney Gary Server attacked the prosecution's DNA evidence during his closing arguments on Tuesday. He said that crime shows on television have given people the false impression about its accuracy, the Philadelphia Inquirer reported.

The defense also argued that Johnson's mental capacity was limited. Their key witness was a neuropsychologist who claimed that Johnson had brain damage, perhaps from birth. His IQ is in the 70s, which is roughly "mentally retarded," Gerald Cooke told the court on Monday.

Johnson's defense reminded the jury of this testimony during closing arguments on Tuesday. Server called Johnson "feebleminded" and said his client didn't understand what he was doing when he confessed to police.