The suicide bomber who killed 101 people inside a mosque at a police headquarters in Pakistan was wearing a uniform and helmet when he staged the attack, a police chief said on Thursday.
Hundreds of police were attending afternoon prayers in what should have been a tightly controlled compound in the northwest city of Peshawar on Monday when the blast erupted, causing a wall to collapse and crush officers.
"Those on duty didn't check him because he was in a police uniform... It was a security lapse," Moazzam Jah Ansari, the head of Khyber Pakhtunkhwa province police force, told a news conference.
Police have a "fair idea" about who the bomber was after matching his head found at the scene with CCTV images.
"There's an entire network behind him," Ansari said, explaining that the bomber had not planned the assault alone.
Authorities are investigating how a major breach could happen in one of the most sensitive areas of the city, which houses intelligence and counter-terrorism bureaus and is next door to the regional secretariat.
It is Pakistan's deadliest assault in several years and the worst since violence began to resurge in the region after the Afghan Taliban takeover in Kabul in 2021.
Authorities are also investigating the possibility that people inside the compound helped to coordinate the attack, a senior city police official said on condition of anonymity on Wednesday.
"We have detained people from the police line (headquarters) to get to the bottom of how the explosive material made its way in and to see if any police officials were also involved in the attack," he said.
The police official said at least 23 people had been detained, including some from the nearby former tribal areas that border Afghanistan.
The assault has put a scarred city on edge, harking back to more than a decade ago when Peshawar was at the centre of rampant militancy carried out by the Pakistani Taliban (TTP) before a clearance operation flushed them into the mountainous border and Afghanistan.
Analysts say militants have become emboldened since US and Nato troops withdrew from Afghanistan and the Taliban swept into Kabul, with Islamabad accusing them of failing to secure their borders.
Security forces have since become the target of increasing low-level attacks, often at checkpoints.
The assaults are claimed mostly by the TTP as well, as the local chapter of the Islamic State, but mass casualty attacks remain rare.
The TTP has distanced itself from the Peshawar mosque blast, claiming it no longer attacks places of worship.
However, police said authorities were investigating whether an occasional affiliate of the group was responsible. (AFP)