Paris : A man was arrested in Paris on Friday suspected of slitting the throats of his father and brother outside a building in the east of the French capital, police sources told AFP.
The circumstances of the attack were unclear.
Some witnesses said the suspect made remarks "linked to radical Islam" but the police urged caution, saying the killer's motives were unknown.
A resident of the high-rise building in the city's 11th district said he heard a man "crying for help" at around 1000 GMT.
"I looked out the window and saw a man lying on the ground. There was a lot of blood.
"There was another man standing beside him, dressed in a white djellaba (loose-fitting tunic worn by some Muslims). He fell to his knees and prayed until the police came to take him away," 21-year-old Thomas told AFP.
Another resident, 64-year-old Francois Petitjean, described a harrowing scene.
"When I arrived in the hall of the building I saw a body lying in a pool of blood, in front of the postboxes. It was carnage. I went out and then saw another person covered in blood," he said, expressing shock.
Police had sealed off a section of the street around the building. No further details on the suspect or the victims were immediately available.
