A man charged with raping a 101-year-old woman has said he did not plan the alleged sexual assault and “would have worn a condom” if he had, according to police.

The 20-year-old from Milwaukee, Winconsin, is alleged to have told police he was planning a robbery of the woman’s home but changed his mind when he saw her in bed.

Antoine Devon Pettis, 20, faces charges of burglary, aggravated battery and second degree sexual assault, which carries a penalty of up to 25 years in prison.

The charge of second degree sexual assault refers to sexual intercourse without consent in the US state of Wisconsin.

Police say the victim was asleep in her home, where she lived alone, when the robbery took place.

She woke up upon hearing a noise and asked who was there, and was told to “shut up” and slapped in the face.

The attacker is then said to have sexually assaulted her and left, according to the criminal complaint. Police arrived to find the woman bleeding; she was taken to hospital for treatment.

Mr Pettis left DNA evidence on the woman’s body and nightgown, according to Milwaukee Police Department’s Sensitive Crimes Division.

The case is unusual because DNA already on file from a relative of Mr Pettis was initially used to determine that the crime had been committed by a family member, due to similarities in the DNA.

This is only the second time in the history of Wisconsin state that such a method has been used.