"I immediately called my friend Colonel Rezaul Kabir who was inside the Bangladesh Rifles (BDR) headquarters," the retired major general said of the events that broke out on February 25.
"He told me, 'You have to do something. About 20 soldiers are shooting at us,' Karim, a 57-year-old former BDR chief, said.
He was one of the last people to speak to Kabir, who was gunned down by BDR soldiers along with more than 70 other mostly senior military men during a 33-hour standoff at the three-square-kilometre (1.2-square-mile) compound.
Their bodies – disposed of in sewers and shallow graves – were discovered in the days after the bloodshed ended, with an estimated 1,000 guards apparently fleeing in civilian dress.
Tensions in the BDR, the paramilitary force that patrols Bangladesh's border with India and Myanmar, had been simmering for months over troops' demands for more pay, better conditions and a change in command structure.
Most senior BDR officers are seconded from the army for two to four years and border guards, who earn around $70 (Dh258) a month, complain they cannot get promotions, and that their grievances are not heard.
But many Bangladeshis cannot accept how a dispute over pay could end so savagely. Five men, including the accused ringleader, have been arrested.
"Despite the soldiers' grievances there comes a point where you think it must be intruders from outside. The brutality of this is unheard of," Karim said, adding that he believed most BDR troops who opened fire had not helped plan the mutiny.
"When there is an uprising it is easy for rank-and-file soldiers to get caught up in it. Not all BDR soldiers are rebels."
In April 2001, when Karim was in charge of the BDR, 16 Indian troops and three Bangladeshi soldiers were killed in one of the bloodiest clashes on the shared border.
"This may be revenge for what happened in 2001," Karim said. "There is a conspiracy. Our neighbours don't want our army and our BDR to be strong."
India and Bangladesh have traditionally enjoyed warm ties – with newly elected Prime Minister Sheikh Hasina often criticised by anti-Indian quarters for her close relationship with the bigger neighbour.
The Indian media, meanwhile, has said a politician from the opposition Bangladesh Nationalist Party (BNP) with close links to Pakistan is to blame.
They say the mutiny is aimed at diverting attention away from war crimes trials Hasina has promised to hold against the Bangladeshis who sided with Pakistan during the country's bloody nine-month war of independence in 1971.
Others have accused Muslim extremists, with some pointing the finger at Islamic political party Jamaat-e-Islam, which has condemned the attacks.
Ataur Rahman, a professor of politics at Dhaka University, said the conspiracy theories could prevent the truth from emerging.
"If you confuse people the truth never comes out. We are currently heading for a state of confusion," he said. "It's a difficult and messy situation."
The violence has raised fears for the survival of Hasina's civilian government, which took over from an army-backed regime little more than two months ago, exposing deep tension between the elected leaders and the military.
The army has launched its own investigation into the killings.
It was reportedly furious with Hasina's promise of an amnesty – on which she later backtracked – for mutineers who surrendered, and her refusal to use force to end the revolt.
"We have to find out what happened, that's the duty of the government and the military, but in reality the full truth may never emerge," Rahman said.