After night shots in California with six dead and twelve injured at the weekend, the police caught a suspect.
A 26-year-old man was arrested on allegations of assault and illegal possession of a gun, the Sacramento police said on Monday afternoon (local time).
Police Chief Kathy Lester told KCRA that the investigation was "complicated".
One assumes several perpetrators.
More than 100 shell casings were found at the scene, the police said.
Three men and three women between the ages of 21 and 57 were shot dead in the Californian capital Sacramento on Sunday night.
Authorities announced the identity of the victims on Monday.
Unknown persons opened fire around 2 a.m. in a nightlife area in the city center.
The shots were preceded by a major argument, Lester said on Sunday.
Eyewitnesses reported chaos and panic in the neighborhood as people fled or took cover, the San Francisco Chronicle reported.
Firearm attacks with multiple deaths occur again and again in the United States.
According to a count by the Gun Violence Archive website, around 45,000 people were killed by gun violence nationwide last year.
Suicides were also counted.
Since the beginning of the year, the website has already recorded 10,700 deaths.
The right to bear a gun is a highly controversial issue in the United States.
Attempts to tighten the lax gun laws repeatedly fail due to resistance from conservative Republicans and the influential gun lobby.