A 77-year-old woman suffered a fatal stab wound while trying to break up a sword fight Thursday between her grandson and brother-in-law, police said.

An autopsy determined Franziska Stegbauer died of a wound from one of the swords, police Sgt. Matthew Mount said. Both men were hospitalized with stab wounds and one was critically hurt.

"We're unsure yet who started this fight, how the swordplay got involved," Mount said. "We're not sure who it was who stabbed the woman. We'll have to do some testing on the swords and figure out who had which sword, whose blood is on which sword."

One of the weapons was a World War II-era Japanese officer's sword with a thin blade, and the other had a thicker blade, Mount said.

Police placed Stegbauer's grandson, 39-year-old Chris Rondeau, under arrest on a preliminary charge of attempted murder. Stegbauer's brother-in-law, 69-year-old Adolf Stegbauer, suffered several serious stab wounds, police said.

Franziska Stegbauer was not breathing when officers arrived about 1 a.m. at the home on the city's northwest side and she was later pronounced dead at a hospital, police said.

Adolf Stegbauer was listed in critical condition at Wishard Hospital, a spokesman said.

Rondeau also was taken with stab wounds to Wishard. Police said he was alert at the scene, but a condition update was not immediately available. He was being held in the hospital's detention unit.