A 78-year-old Bismarck man has been formally charged with killing his wife, who authorities said was struck on the head.

Matthias Zimprich is charged with murder in the death of his 74-year-old wife, Ludwina, sometime Monday night or Tuesday morning.

Authorities said the couple had been married more than 45 years. Zimprich's attorney, Al Wolf, said Matthias Zimprich was being treated for cancer.

An autopsy showed Ludwina Zimprich died of "multiple blunt force injuries to the head," Burleigh County prosecutor Richard Riha said. No weapon has been identified but it appeared to have been some sort of heavy object, he said.

Judge Bruce Romanick ordered Zimprich held without bail after Wolf and prosecutors said he was a suicide risk.

Zimprich told the judge he had owned a trucking business and had been retired since 1985.

Neighbors were shocked at the killing, saying the couple were always together and that they saw no sign of problems.