In broad day light, bike-riding criminals gunned down a jail guard yards away from the gate of the country's largest high-security prison in Kashimpur of Gazipur yesterday.

About-to-retire sergeant instructor Rustam Ali was sitting in front of a pharmacy about 150 yards from the prison gate when two to three assailants on a motorbike shot him from close range around 11:15am, said locals and the prison authority.

He fell to the ground and died on the spot. The criminals fled towards Dhaka-Tangail highway on the motorbike.

Locals who saw his body immediately after the incident said his right hand was on the left side of his chest. Possibly he was trying to apply pressure on the gunshot wound. Blood was also gushing out of his head.

Rustam was not in uniform.

Police reached the spot about an hour later, said some locals. They sent the body to Shaheed Taj Uddin Ahmed Medical College morgue in Gazipur for an autopsy.

Abdus Salam, residential medical officer of the hospital, said Rustom was shot in the left of his chest and left cheek. Two bullets were inside the body.

Rustam served as the chief prison guard at Jail-1 before he went on leave preparatory to retirement (LPR) a few months ago, said Inspector General of Prisons (IGP) Brig Gen Syed Iftekhar Uddin.

The body was handed over to the prison authority in the afternoon after the autopsy. The prison authority suspected that there might be a militant link in the killing.

Delwar Hossain, superintendent of police in Gazipur, said they would look into any possible militant links.

He said police picked up at least seven people, including Rustam's wife Nasrin Akter, Sohel Rana, husband of Rustam's adopted daughter Nahida, and owner of the pharmacy Saiful Islam, who was at the shop, for questioning.

The SP said they would investigate whether any family dispute was behind the murder.

The police official said Rustam had bought land and built a house in the area a couple of years ago.

He, however, was living with his wife at the staff quarters inside the jail compound, said jail authorities.

Briefing media near the spot in the afternoon, IGP Iftekhar said preliminary probe suggests the killing “seems to be planned”.

He later said it seemed the killers were professionals. The crime scene was beyond the jurisdiction of the jail authority and that it was not possible for the jail staff to react immediately.

He said Rustam had served as prison guard at some of the jails where militants had been kept. Rustam was the chief prison guard of Jail-1 where most of the convicted militants are kept.

The IGP said in their attempts to control the convicts, prison officials at times had disputes with them.

“Whether he developed any enmity with the militants kept inside the jail or any of their groups outside need to be investigated,” said the IGP.

Rustam was promoted to sergeant instructor two weeks before he went on LPR. He was transferred to the female jail in Kashimpur in November last year, the IGP added.

According to him, a murder so close to the prison was “of great concern to the prison authority and the public”. The jail authorities all over the country have been instructed to beef up security.

The jail authority said Rustam was born in 1956 in Pirojpur and raised in Comilla. He joined work in 1974. He had not fathered any children.

Before joining Kashimpur jail, he served at Barisal jail.

Locals said the place where he was killed is the busiest place in the area and Rustam did his daily shopping from there.

Shop-owner Mominul Haque who knew Rustam in person said as far as he was concerned, Rustam had no enmity with anyone.

The prison authority formed a three-member committee, led by Deputy Inspector General (prisons) Golam Haider of Dhaka, to probe the incident and asked the committee to submit a report in seven working days, said Iftekhar.

Alongside local police, members of Rapid Action Battalion and Police Bureau of Investigation (PBI) collected evidence from the spot.

Joydevpur police said no case was filed in connection with the killing as of 11:00pm last night.

In February, 2014, an armed gang ambushed a prison van carrying militants from Kashimpur jail to Mymensingh and took three convicted members of banned militant outfit Jama'atul Mujahideen Bangladesh in Trishal of Mymensingh.

Two of them were on death row.