A man arrested on suspicion of killing a photo shop owner and his son and critically wounding his wife with a cutting tool has told police he had had trouble with the son, investigative sources said Monday.

Hironobu Ito, 24, was arrested Sunday after breaking into the home of photo shop owner Nobuyoshi Ito, 60, in Iide, Yamagata Prefecture, earlier in the day. Earlier reports said he and the victims are distant relatives.

The shop owner and his 27-year-old son, Satoru, were taken to a hospital, where they died of stab wounds, police said. The owner's 54-year-old wife, Hideko, was in critical condition.

During questioning by police, the suspect said he entered the couple's bedroom unaware that it was their room, the sources said.

Based on the suspect's statements, police believe he held a grudge against the son that eventually led to the indiscriminate attacks against other members of the family, the sources said.

According to police, the suspect entered the house through the front door, which was not locked.

After entering the house, he first attacked the wife. The husband, who was sleeping next to his wife, woke up and tussled with the suspect but was stabbed more than 10 times.

Soon after that, the son, who came down from the second floor, was stabbed, police said.

The suspect told police he threw away the weapon in the mountains.

On Monday, police mobilized 60 officers to look for the weapon.

Satoru Ito, who worked in the city of Yamagata, was in Iide for the Golden Week holidays, which ended Sunday.

He was scheduled to get married in October in Hawaii and frequently returned home to make arrangements for his wedding, according to people close to him.