"We don't expect to reveal the crime within few hours," police commander Maj. Gen. Ashraf Rifi told Future TV. "The investigation is like a puzzle. You collect the pieces and put them together in a logical way."
Al-Hassan had many potential enemies.
Besides his investigation of Samaha, al-Hassan helped investigate the 2005 assassination of former Lebanese Prime Minister Rafik Hariri, a powerful Sunni figure. An international tribunal indicted four members of Hezbollah for Hariri's killing, although the group denies involvement.
His department also had a role in breaking up several Israeli spy rings inside Lebanon in recent years, Lebanese officials said.
Al-Hassan, 47, who was married with two children, is expected to be buried Sunday next to Hariri's tomb in downtown Beirut. His family arrived in Lebanon on Saturday on a private plane from Paris, where they live.
Lebanon's top Sunni cleric, Grand Mufti Mohammed Rashid Kabbani, condemned the assassination, calling it a "criminal explosion that targets Lebanon and its people." He also called for self-restraint, saying "the criminal will get his punishment sooner or later."
But many Lebanese were seething with anger.
In the eastern town of Marj, protesters tried to storm an office of the pro-Syrian Itihad group. Lebanese soldiers pushed them away, wounding five protesters, security officials said. Dozens of people who marched in protest in the border town of Moqueibleh came under fire from the Syrian side of the border, forcing them to disperse, the officials said.
The highway linking central Beirut with the city's international airport was closed, as well as the highway that links the capital with Syria, the officials said.
In the predominantly Sunni northern city of Tripoli, gunmen were roaming the streets on motorcycles and opening fire in the air.
The army issued a statement urging Lebanese to overcome the crisis and coordinate among themselves in order to give a chance to the "the criminal killers who tried through the crime to incite strife and split the country."
Associated Press writer Barbara Surk contributed to this report.
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