British Chris McManus and Italian Franco Lamolinara were killed by the suspects as Nigerian soldiers and the British Special Boat Squad (SBS) stormed a house in Sokoto to rescue the foreign engineers.
They had been in captivity since their abduction inBirnin Kebbi,the Kabbi State capital, last May.
Five men were arrested in connection with the abduction and killing of the duo.
Among them is Abu Muhammed believed to be the ring leader of the group and a factional leader of the Islamic sect, Boko Haram.
They were moved to Abuja yesterday by security agents for interrogation.
The suspects,sources said, told their interrogators that they were under instruction of their leaders to shoot the hostages whenever they came under any threat from security agents.
One of the suspects was quoted as having said : “We had a standing instruction to kill the hostages immediately we sight security agents around the building.
“We were to kill the hostages since we were not sure of being alive after an encounter with security men.”
However, a faction of the sect yesterday denied involvement in the abduction and eventual murder of the Briton and Italian.
According to an international cable television, a source informed that an un-named Boko Haram spokesman called a Nigerian journalist in Sokoto to tell him that the Islamic group had no hand in the incident.
The cable television stated that the Boko Haram faction spokesman claimed that they had never been involved in kidnapping and would never do it for the purposes of extortion. It maintained that for now, bombing its targets remained its major strategy and had no intention of changing it.
Senior security sources yesterday said a desperate call by a Boko Haram member during a gun battle with Abu Mohammed and others in Zaria might have led to the retaliatory killing of the hostages in Sokoto.
Investigation by our correspondent revealed that the Thursday operation was coordinated by the State Security Service (SSS) and the military in conjunction with British secret agents.
It was gathered that it had been difficult to locate the whereabouts of the hostages in the last 10 months because their captors kept relocating them at the slightest suspicion of security tracking.
The SSS,it was gathered, however, recorded a breakthrough when it located Abu Mohammed and some other leaders of the sect in Zaria , Kaduna State.
A reliable source said: “Those arrested in connection with the abduction and killing of the hostages have been moved to Abuja for interrogation. I mean Abu Mohammed and four others.
“They are being quizzed to know their motive, why the hostages were killed and the Al-Qaeda connection. This probe has international dimension to it because Britain and Italy will want to ascertain why their citizens were targets.”
Giving an insight into the operation ,the source said : “The operation to free the hostages was conducted in Zaria and Sokoto.
“Having established that Abu Mohammed faction abducted the hostages, the SSS conducted a comprehensive investigation which led to the uncovering of his hideout in Zaria on Tuesday. While he was in Zaria , this leader made sure that the hostages were kept in Sokoto.
“Following the finding of the hideout, the SSS, supported by the military, succeeded in invading the place and arrested Abu Mohammed and four leaders.
“The moment the game was up, one of those arrested was chosen to lead security agencies to the compound in Madera Quarters in Sokoto where the hostages were kept.
“At that point in Zaria , the first leg of the operation by the SSS and the military achieved 100 per cent success.
“Concerning the operation in Sokoto, we are probing a clue that during the gun battle in Zaria , one of the Boko Haram members made a phone call to Sokoto that their leaders were under siege.
“This theory of phone call is being analysed to know whether it is true or not.
“You know the operation in Zaria was a heavy crossfire, Boko Haram was humbled. I think the phone call made those in Sokoto to become desperate to kill the hostages.
“The operation would have been like that against Osama Bin Laden in Pakistan .”
A top government official said: “The British Government was involved in this operation and their security operatives were convinced that the SSS, the military and other agencies gave their best to free the hostages.
“It is obvious that the sect is deadly and we all have to be a step ahead. I mean the international community.”