Paris Attack Manhunt: Search Continues on Day Three After Massacre

Paris Attack Manhunt: Search Continues on Day Three After Massacre, The manhunt for two brothers believed to be behind the deadly terror attack on a French satirical magazine entered a tense third day on Friday, with more than 100,000 security personnel on guard and more still searching for Cherif and Said Kouachi.

A third suspect in the attack that left 12 people dead in the Paris offices of magazine Charlie Hebdo, 18-year-old Mourad Hamyd, surrendered late Wednesday at a police station near the French-Belgian border.

SWAT teams with weapons drawn swept house to house on Thursday in the northern French countryside after a sighting of the brothers was reported at a gas station in the town of l'Aisne. Helicopters circled above the rural villages as the teams fanned out and van after van of masked and armed officers rolled through small farmtowns and took up positions on highways and main roads.

Authorities are keenly aware that at least one of the brothers has had military training. Said Kouachi, 34, traveled to Yemen in 2011 to be trained by al-Qaeda in the Arabian Peninsula, two senior U.S. counterterrorism officials told NBC News on Thursday. The training lasted for several months, one of the officials said.

After winding down for the night, the manhunt is expected to resume and grow in numbers and intensity of resources on Friday morning. Officials continue to pore over phone and internet records for clues.

French Interior Minister Bernard Cazeneuve said 4,000 military personnel would join the nearly 88,000 security personnel already mobilized in wake of the threat on Friday.

"I would like to tell the French people that the government has taken steps to secure their safety," he said in a statement on Thursday

While the hunt for the suspects was focused largely on countryside Paris remained on its highest security alert level with an extraordinary force of police in public areas.