Suweisi headed both the Tripoli Security Directorate and National Security Directorate.
He was shot and killed Tuesday as he and some colleagues left a meeting in Tajoura. "On his way back from Tajoura, their vehicle was ambushed at a traffic light by two cars with armed men," Ministry of Interior spokesman Rami Kaal told the BBC.
When Suweisi refused to exit the vehicle, the armed gunmen opened fire, fatally shooting the police chief in the head. His two colleagues, who exited the vehicle, were kidnapped.
Violence between depleted government forces and Islamist militant gangs has escalated in Libya in recent weeks.
Fighting in and around the capital forced many embassies and international organizations to shutter.