Reuters/Karachi
Pakistani Navy officials show the cap of Lieutenant Yasir Abbas who was killed during battle against attackers at  Navy base, in Lahore yesterday
Pakistan was yesterday investigating a brazen assault on a naval base in Karachi, raking over clues in a bid to identify the attackers who carried out the siege, two of whom may have escaped.

It was the worst assault on a military base since the army headquarters was besieged in October 2009, piling further embarrassment on the armed forces three weeks after Osama bin Laden was found living under their noses.
“A joint investigation team has started the investigation,” one security official said on condition of anonymity.
Up to six Taliban fighters, armed with rocket-propelled grenades, explosives and automatic rifles, crept under cover of darkness to place ladders against the walls of the Mehran base and climbed over barbed wire into the facility.
In a 17-hour standoff they managed to destroy two P-3C Orion surveillance aircraft, costing an estimated $36mn, which had only been delivered by the US a year ago, and killing 10 security personnel.
Although the Pakistani Taliban claimed responsibility, government official Sharfuddin Memon from the southern province of Sindh, of which Karachi is the capital, said the attackers had not yet been identified.
Security officials say they are piecing together how the well-planned attack unfolded and how the attackers worked hard not to be spotted.
“We have not found any video. The attackers succeeded in dodging the cameras,” one official said.
A reporter saw stepped up security around the Mehran base yesterday while visitors were barred from a nearby Pakistan Air Force museum.
A Pakistani Navy commando was the first to detect Taliban militants attacking a naval aviation base on Sunday night. He was dead within seconds.
The small group of militants, as few as six, who attacked the base gave its defenders no time.
“You cannot imagine how quick they were,” said a Pakistani security official who asked not to be named. “When they entered, one of the Navy commandos saw them and tried to react.”
He never got the chance.
“It was a single shot in the darkness which took his arm off,” the official said. “You can imagine how good they were.”
The commando died on the spot.
It was about 10.30pm when he died, and the violence didn’t end until 16 hours later on Monday afternoon.
The Al Qaeda-inspired militants bent on avenging Osama bin Laden’s death at the hands of US special forces on May 2 killed 10 Pakistani troops and wounded 20.
It took about 100 commandos, rangers and marines to kill four militants and recapture the base, further humiliating the military. Two militants are believed to have escaped.
The attack calls into question the military’s ability to secure the country’s borders and nuclear weapons.     
How did the militants get into one the country’s most heavily guarded bases and hold off commandos and soldiers for so long?
Some security officials said it must have been an inside job because of the obstacles to entering. The attackers probably travelled along a dirt lane running beside cinder block shacks at the rear of the base.
In order to get in, they had to cross a long, thick sewage path, elude guards in towers, set up a ladder, scale a 12-foot wall, and cut through barbed wire.
The security official said the assailants were dressed in black with night-vision goggles and armed with Russian hand grenades, rocket launchers, assault rifles and suicide vests.
They fired rocket-propelled grenades at aircraft and fuel tanks, sending huge flames into the sky.
Within a short time, a rapid reaction force from the base tried to engage the raiders, but they retreated to a main building at the sprawling base where they would hole up for the rest of the siege.
Who were these militants?
The security official said the militants looked foreign, with fair complexions, perhaps Chechens or Uzbeks. Foreign militants tied to Al Qaeda’s international network are known to train in Pakistan’s unruly tribal areas along the Afghan border.  Many of them are allied with the Pakistani Taliban. 
By 2.30am on Monday, the initial fighting had ebbed. As jet fuel burnt around them, both militants and the military were looking for a plan.
Commanders didn’t want to launch a full-scale assault because they feared further damaging aircraft and infrastructure. Fires had already claimed hangars and damaged other aircraft. 
“If we had tried to kill them quickly they might have blown themselves up near our assets and caused more damage. We did finally manage to push them away from our assets,” said an intelligence official.
The militants’ plan was direct: Kill, and be killed.
Pakistan officials say the main operation to retake the base was over by 9.30am, followed by a search and clear operation lasting until the afternoon. There was scattered gunfire and occasional explosions throughout the day.
“Clearly there was a (security) breach,” said another security official. “In my personal view there had to be some help from the inside - to brief the militants about the area, and location.” 
“Our forces should have done better. But at the end of the day, if there are suicide bombers who have already decided to die, I don’t think you can stop them,” said Shabbir Hussain, a car dealer who lives behind the base.
The civilian government has called a defence committee meeting for today, two days after the assault, showing a surprising lack of urgency.
The military has remained silent.  But Pakistanis are more anxious than ever.