A terrorist caught alive is not deniable. One can deny oral, documentary and technical intelligence as fabricated, but one cannot deny someone caught in flesh and blood.
By capturing Ajmal Kasab alive and in flesh and blood, the Mumbai police made certain that neither the Lashkar-e-Tayiba nor Pakistan's Inter-Services Intelligence, the Lashkar's handler, will be able to deny convincingly the Lashkar's involvement in the 26/11 terrorist strike in Mumbai. He is the living proof of the Lashkar's involvement.
And the journalist, who photographed him moving around with his accomplice in the railway terminus killing people with his gun, recorded undeniably his role in the perpetration of the dastardly crime.
If Kasab's capture and his interrogation proved the Lashkar's involvement in the terrorist strike, the photographs proved his involvement in killing dozens of innocent civilians.
His interrogation enabled the police not only to re-construct the entire conspiracy mounted by the Lashkar and its handlers in Pakistan, but also identify the conspirators based in Pakistan headed by Mohammad Sayeed, the Lashkar leader.
The monitoring of the telephone conversations between the perpetrators in Mumbai and their handlers in Pakistan produced a wealth of technical evidence about the role played by the Pakistan-based conspirators in the orchestration of the terrorist strike. But without the corroborating details provided by Kasab, it might not have been possible to identify them by name and force Pakistan to arrest them.
If Kasab had not been caught alive and interrogated, Pakistan might have rejected the intercepted telephone conversations as unlinkable to specific individuals. It is Kasab's interrogation that provided the link between the recorded voices and the persons to whom those voices belonged. Kasab knew those persons and recognised their voices.
The reconstruction of the crime and the identification of the Pakistan-based conspirators by the Mumbai police with Kasab's help forced Pakistan to arrest and prosecute the persons identified by Kasab.
A group of ten fidayeen (suicidal attackers) from Pakistan had mounted the attack. The instructions to them by the Lashkar were not to get caught alive. Nine of them died during the execution of their attack. If Kasab had also died, the Mumbai police might still be struggling to successfully investigate the case.
There was total confusion in Pakistan when they heard that Kasab had been caught alive thereby depriving them of the protection of deniability. Even then, they tried to deny their involvement by claiming that Kasab was not Pakistani. But after some journalists in Pakistan traced Kasab's family in his home village in Pakistani Punjab and interviewed them, even this fig leaf of a deniability was not available to them. They had to admit that the terrorist strike had been mounted from Pakistan by the Lashkar.
Kasab's interrogation provided the police and the intelligence agencies with a lot of information as to when and how the terrorist strike was planned, who were the people recruited, where were they trained, what kind of training they received, who were the people involved in training them, what instructions were given to them before they left Karachi for Mumbai etc.
Such details would have enabled the investigating and intelligence agencies to strengthen their data base on the Lashkar and to understand better how it functions.
But Kasab was only a foot jihadi -- trained to carry out a terrorist strike and die in the process. He was not from the Lashkar's leadership core. His knowledge was confined to details of the terrorist strike of 26/11. He had no knowledge of the future plans of the Lashkar and of its sleeper cells in India, including the identities of the Indian Mujahideen members in India helping the Lashkar.
While he was helpful in the investigation and reconstruction of the terrorist attack of 26/11, he was of no use in detecting and neutralising Lashkar's sleeper cells and the Indian Mujahideen. His utility in anticipating and thwarting the Lashkar's future strikes will be almost nil.