MINNEAPOLIS — Prosecutors on Wednesday charged a 22-year-old man with fatally stabbing his mother and teenage nephew in their Minneapolis home with what police suspect was a samurai sword.

Ishmael Roberts was charged in Hennepin County District Court with two counts of intentional second-degree murder in the deaths early Monday of his mother, 57-year-old Beatrice Wilson, and her 14-year-old grandson, Peter.

The victims’ bodies were found in upstairs bedrooms and had suffered “multiple severe lacerations,” according to the criminal complaint. Minneapolis Police Capt. Amelia Huffman said it was clear from the victims’ injuries that the two had fought for their lives.

A motive for the killings was not known. Hennepin County Attorney Mike Freeman said there have been indications of Roberts being mentally ill.

Roberts has not spoken with investigators since his arrest in Iowa, police in Minneapolis said.

Police recovered a sheath for a samurai sword at the home. As of Wednesday afternoon, police had not located the weapon.

According to the complaint, a resident of the home told police that Roberts had not been in contact with his mother or others in the family for about two years.

Roberts showed up unexpectedly at the Minneapolis home at about 3 a.m. Monday. One of the residents said he tried to speak with Roberts but that Roberts would not talk.

Another witness said he awoke in the house and saw a man wearing a mask and dark clothing stabbing Wilson. As he ran from the house to call 911, the witness said he heard the boy screaming.

Roberts was arrested in Iowa that night after authorities say he rolled Wilson’s car and ran away. Police in Waterloo, Iowa, reported finding blood inside and on the outside of the car, and Roberts’ bloody gym shoes were recovered from a garbage can at a Target store. Investigators retrieved a bloodied floor mat, suspected of being from Wilson’s car, from a trash bin behind the strip mall where Target is located.

Roberts remained jailed Wednesday afternoon in Waterloo. It was not clear if he had an attorney yet in Minnesota. The public defender’s office in Waterloo was assigned to represent him in Iowa, but no one could be reached at the office after business hours Wednesday. A preliminary hearing in Iowa is set for Nov. 9.