Mexican police are questioning an alleged hit man linked to a drugs gang, who was captured after a car chase and shootout in the city of Tijuana.
Mexican police say they seized weapons and ammunition
Mario Alberto Rivera Lopez was arrested with several suspected accomplices.
Police are investigating whether those arrested were behind Tuesday's killing of the editor of a Tijuana newspaper renowned for reporting on drugs gangs.
Mexican and foreign journalists have condemned the murder of Francisco Ortiz, shot in front of his children.
The operation leading to Mr Rivera's arrest began when Tijuana police started following an armoured car that aroused their suspicions, officers said.
The trail turned into a car chase through the city, ending up in a shopping centre where, after a fierce gunfight, officers detained Mr Rivera and several others.
Several weapons, including assault rifles and machine-guns, were seized.
Mr Rivera, also known as "El Cris", is accused of being a hired killer for the Tijuana-based Arellano Felix drugs cartel, which authorities blame for the murder of scores of police, officials and journalists, as well as drug-trafficking rivals.
Investigators said they were looking at whether the drug gang had any links with the shooting of Francisco Ortiz, one of three editors of the weekly Zeta newspaper.
Zeta is renowned for reporting on the influence of drug traffickers in Tijuana, a city on the US border.
There have been several attacks on Zeta's staff, including the murder of its founder 16 years ago.
Officials in the Mexican state of Baja California said Mr Ortiz had just left a clinic with his two children, aged eight and 10, when men passing by in a pick-up truck opened fire on him.
Journalists' groups and human rights organisations both in Mexico and abroad have expressed shock and outrage at his death.