KARACHI, Jan 13: Terrorists who use improvised explosive devices (IEDs) to carry out bombings across the country have changed their modus operandi in Karachi — they increasingly use IEDs hidden inside cement blocks and curve stones.

Elsewhere, they usually use explosive-rigged vehicles and suicide jackets.

These IEDs were used in about eight blasts in Karachi while close to a dozen similar IEDs were detected before they went off and defused by the bomb disposal unit of Karachi police, according to officials.

“Protruding wires or other material visible from inside the cement block or curve stones have led to most of the detections,” said CID SP Raja Umar Khattab.

A 30kg IED concealed in a curve stone was detected in October 2011 by a boy. He was busy washing his car when his eyes caught sight of some wires protruding from a curve stone. The boy got suspicious and informed police, he recalled.

The boy was rewarded by the then IG of Sindh for helping the police.

The same type of IED was found planted near a mosque in the Jinnah Postgraduate Medical Centre in June 2011. It had more or less the same weight as the others found previously and the outer cement covering appearing like a brick.

Brick IEDs were used in two of three attacks on the Naval buses in April 2011 but in the third attack in the DHA an explosive-laden motorcycle was used, he said.

Likewise in December 2011 blast, a brick-covered IED was planted near the Rangers mobile close to Safoora Chowrangi.

The Karachi police got their first chance to lay hands on a brick-covered IED during the 11th of Muharram in 2009 when the device fell from some vehicle in Shadman Town while being transported somewhere.

The chance discovery led to the arrest of six suspects behind the Ashura blast in 2009 and the 8th and 9th Muharram low intensity blasts.

But just six months after their arrest they fled the City Courts in June 2010. One of them later died when a hand-grenade he was carrying blew up in his hands.

The suspects were said to be activists of ‘Jundullah’, a previously little known militant outfit.

They were never rearrested and the police conveniently put the blame for the attacks on Rangers and Naval buses on a splinter group of Lashkar-i-Jhangvi led by Naeem Bukhari.

Bukhari is once reported to have been detained by a law enforcement agency several years ago. He was booked in a drug case, which never proved and was set free for want of evidence, said a law enforcement official.