A 23-year-old boarder in a Tioga rowhouse killed the 92-year-old homeowner, his companion, and her brother last week, then continued living there for at least another day while stealing items including credit cards and televisions, police said Thursday.

Tahzay Young was arrested Wednesday afternoon at 16th and Chestnut Streets after detectives traced the credit card of the elderly victim, Warren Harrison, and saw that it had been used after Harrison’s death to buy clothes and food and to rent a room at a City Avenue motel, Homicide Capt. John Ryan announced at a news conference.

Ryan said police believe Young committed the murders on Nov. 29 or last Friday, fatally stabbing 60-year-old Khadijah Abdullah in a second-floor bedroom of the house in the 1900 block of West Venango Street, and beating her brother, Earl Cottle, 57, and Harrison on the first floor before taking the three victims' bodies into the basement.

The victims were found Saturday after Harrison’s daughter went to the house, noticed it in disarray, and called police. Ryan said responding officers found that all three victims had been covered in blankets in an apparent attempt to conceal their remains.

Police Commissioner Richard Ross, who also attended Thursday’s news conference, called the crime “sick” and “vicious.”

Harrison’s granddaughter, Kimberly Ringgold, 38, said on Thursday, “I am devastated. Truly devastated.”

According to Ryan, Young had moved in with Harrison — well-known in the neighborhood for his gardening — at some point after July, when he was released from jail. Court records say that he had been charged with theft in 2014, and that bail had been set and revoked several times since. But details of his case were not clear Thursday. According to court records, he also was found guilty of a summary offense of theft in February.

Ryan said that it was not clear how Young had come to live with Harrison, but that Harrison had been trying to evict him, which likely played a role in the killings.

Police do not believe anyone else was involved in the crimes. Ryan said: “It is our understanding that Mr. Young acted alone."

Ryan said Young was to be charged with three counts of murder as well as robbery and related offenses. Charges were pending Thursday afternoon.