First, lets look at what the judgement says. It only convicted Sanjay Dutt for illegal possession of Arms and exonerated him of any involvement in the conspiracy of the blasts. Hence his self defense reason sounds valid and the courts were unable to link the weapons to the the blasts so he was awarded just a 5 year sentence.

Now covering the article by Shekhar Gupta, the journalist who was covering whole scenario then in 1993. On one issue there is no doubt: the firearms given to Sanjay Dutt in the middle of January 1993 were indeed for self-defense. So what is anybody complaining about? Self-defense is as good a defense morally as in a court of law.

The problem, as usual, lies in the below detail.

The serial bombings, Mumbai seemed like a flawless operation, it was a disaster strategically. Because the objective of its planners was not merely to kill a few hundred people. It was to orchestrate communal riots of an unthinkable intensity nobody would be able to control. It was the first ISI operation of this scale anywhere in India.

The key to understanding that plot lies in separating, analyzing and sequencing three different sets of events. The first riots broke out on December 6, just as Babri fell. Angry Muslims hit the streets first, and then they faced the full fury of the Shiv Sainik’s and the rest, and an openly partisan Bombay police. These riots settled by the third week of December.
The second round began in the first week of January. But a few significant things had happened in the interim.

First, a large consignment of arms, ammunition and RDX landed at a place called Dighi on the Konkan coast in the first week of January. Second, several key officers I met then told me that bodies of poor Hindu Mathadi (head-load) workers from the Maharashtra hinterland were being found early mornings on streets where they often slept, slit at the throat with a small knife as if in some ritualistic style. That was, however, an analytical afterthought as the investigators pieced the story together. These bodies were mostly found around Dongri, a communally sensitive area. The conjecture was that someone was trying to provoke a second round of riots. That there was a plan to this.

The armaments were being landed at the same time and were to be distributed, again, in “sensitive” areas. Sanjay Dutt got his consignment, for example, on January 16, when the second round of riots was ebbing. So the lots of weapons distributed around this time were for “self-defence”, but not for self-defence during those riots. The riots had, by now, ended. The second consignment landed at Shekhadi in the first week of February. There were no riots then. In fact, there was total, if uneasy, peace in Bombay until the bombings on March 12, five weeks later.

Focus on these dates and events and the picture becomes clearer. The mathadis, who are a large, poor but well-knit population, were killed ritually in sensitive areas to provoke fresh riots. Since the Sainiks were now well organised and helped along by a partisan police, this created greater justification for bombings in retaliation and also inspired, for the masterminds, what the Supreme Court just described as the foot-soldiers within the furious and insecure local Muslim population. The second round of riots was much more one-sided (against the Muslims) than the first. It is after this that the weapons were pre-stocked in sensitive localities and the bombings were planned. The plot was simple: the bombings will again unleash angry Hindu hordes, escorted by a partisan police. And they will be greeted by AKs and grenades, leading to mayhem of the kind never imagined. And then the fires will spread all over India.

Sanjay Dutt was in touch with Anees Ibrahim, brother of Dawood Ibrahim
& conclusively involved in their operation. The fact that he is a celebrity clearly helped him.