Abdellatif Merdas, a Moroccan member of parliament, has been shot dead in Casablanca, according to police.
The 53-year-old, a politician with the liberal Constitutional Union party, was gunned down late on Tuesday near his home in the well-off southern district of Californie.
His assassins fled the scene, but police said on Wednesday they had arrested a 27-year-old man suspected of links to the assault.
A raid on the suspect's home came up with two shotguns similar to the one used in the attack, police said.
The assault is believed to be criminally motivated.
Initial investigations suggest that the suspect had previously threatened Merdas with death due to alleged personal differences, police said.
Merdas, who represented the Ben Ahmed district 60km south of the coastal city of Casablanca, was in his official car when he was hit three times by shotgun fire, private news websites reported.
Hit in the head, he succumbed to his wouds shortly afterwards.
Local news websites showed photos of the scene and a car with broken windows, surrounded by police officers.
They said one or more attackers fled in a foreign-registered vehicle.