PARIS (AP) — Four children between nine months and 10 years old and their mother were killed in their apartment east of Paris, in what the local prosecutor called an exceptionally violent crime. Authorities said the children’s father was arrested Tuesday and is the primary suspect.

Neighbors spotted a pool of blood outside the family’s door on Christmas Day and alerted police, who discovered the five bodies, Prosecutor Jean-Baptiste Bladier told reporters in the city of Meaux.

The mother and two daughters, ages 7 and 10, were stabbed several times overnight from Sunday to Monday, he said. The couple’s two sons, ages 9 months and 4 years old, were suffocated or drowned. The prosecutor described a small, blood-stained apartment in extreme disarray.

The motive for the killings was unclear. The suspect, a 33-year-old man born in the Paris suburb of Colombes, was arrested Tuesday outside his father’s home northeast of the French capital, the prosecutor said.

The suspect had stabbed his partner once before, when she was pregnant with their older son in 2019, but the investigation was dropped because he was declared mentally unsound at the time of the attack, the prosecutor said. The suspect had been placed in a psychiatric hospital in 2017, and also attempted suicide that year, the prosecutor said.

The couple had been together for 14 years and had known each other since high school, Bladier said.

None of the family members’ names were released, according to French law protecting minors who are victims of crimes.

Authorities are opening an investigation into five homicides, and the suspect will undergo psychiatric examination to determine the next steps, the prosecutor said.