The man who attacked a mosque in the Pakistani city of Peshawar on Monday used a police uniform to gain access to the area, police have said.
The suicide bomber reportedly entered through the main gates of the secure zone where the mosque is located.
Police chief Moazzam Jah Ansari said they had CCTV footage revealing the man’s final movements, and were closing in on the “terror network” responsible.
He also confirmed a head found at the site was the attacker’s.
Monday’s blast – one of the deadliest attacks in Pakistan in years – took place at a 50-year-old mosque in a high-security police zone called Police Lines.
At least 100 people were killed, of whom most were police officers.
Officers failed to check the attacker as they assumed he was one of them, Mr Ansari said. “I admit this was a security lapse. My men could not stop it. This is my fault.”
He explained that police had been able to trace the bomber’s motorcycle journey before the attack using CCTV footage.
As the man parked his motorcycle, he was “in a police uniform and was wearing a mask and a helmet”. After entering the compound, the attacker asked a constable where the mosque was.
Mr Ansari – who heads the force in Pakistan’s Khyber Pakhtunkhwa province – added that ball bearings had been found which were used in a suicide jacket.
He said 10-12kg (22-26lb) of TNT explosives were used in the blast, which caused the mosque’s roof to collapse on the hundreds who were praying in the building.
Police do not believe the man was a “lone wolf”, and have suggested there is an entire network behind him.
A claim that the hard-line Islamist militant group Tehrik-i-Taliban Pakistan (TTP) carried out Monday’s bombing was later denied by the group, which blamed it on the commander of a breakaway faction.
In the past the TTP has refrained from claiming some attacks on mosques, schools or markets, preferring to cast its violence as a war with security forces and not against the Pakistani people.
In recent years attacks by the TTP and other militant groups have been on the rise again in north-west Pakistan after the Afghan Taliban gained power in neighbouring Afghanistan in 2021.
Pakistan says its forces are ready to take on the militants.
But the police remain ill-equipped to fight the highly trained and well-armed insurgents. Recent militant attacks include overrunning police stations – and in some cases, police did not offer resistance.