I am not a diplomat so I won't know the exact answer but I can give you an example of Raymond Davis case where US pressure got him released. Infact you congressis where also Tom tomming India's diplomatic victory in Italian Marine case
One: I may or may not be a congressi, and there is no way for you to know, so stop name calling. I point out ludcirous statements and flawed reasonings wherever I can. That doesn't make me a congressi or anything else. (BTW, as I pointed out before, BJP led govts did not get Sarabjit back either, so why don't you call me a BJPite?)
Now: Do you really think that USA and India have the same leverage over pakistan? Pakistan survives on US dole, NOT Indian. Also, USA's words are backed by it's ability to wreak hellfire on pakistan, while completely remaining unscathed. Can India do that? NO. USA can send bombers or missiles at pakistan, and pak cannot hit USA. Period. US can send several carrier battle groups near and into pakistan, and decimate it into a hundred bits, while pakistani forces cannot reach USA. Neither their missiles, nor ships, nor soldiers, nor planes, or anything else. Does India have that advantage? No.
Tens of thousands of pakistanis live in USA, earn money and send it back home. Do they earn similar foreign remittance from India? A lot of their military goodies are gifted by the US. Does India provide them with anything? What makes you think that just because USA can pressurise them, so can we?
I find it so ludicrous when people naively say "Look what USA did, we should do that too!". India is NOT the USA, and there are a thousand things that are impossible for India to do, that the USA can do with ease. Accept the reality.
Just accept it, and admit the fact that you have NO CLUE what our diplomats could have said, to get sarabjit singh back. That's the same spot that our diplomats are in too. They know that tough talking to pak won't get back SS.
All nations are not equal, whether economically, or by military strength, or diplomatic clout (which comes from various factors, economic, military, geopolitical etc) or by HDI. We simply cannot do everything that the US does.