A court in New Delhi acquitted former telecommunications minister A Raja in the country's biggest graft case, which investigators alleged had cost the government as much as $4.8 billion. All others involved in sale of airwave licenses in 2008 were also acquitted.
With eight states going to polls in the coming year, the verdict is seen as a blow to PM Modi's Bharatiya Janata Party, which has won a series of elections since 2014 capitalizing on corruption charges against the previous Congress-led government.
It may prompt PM Modi to hunt for fresh issues going into the state elections before seeking re-election in 2019.
"This is a very awkward moment for Prime Minister Modi -- his entire campaign was built around allegations about this multi-billion scam and that the previous government was corrupt," said Nilanjan Mukhopadhyay, a political analyst and author of a biography on PM Modi.
This week PM Modi returned to power in his home state Gujarat, but it was a hard-fought battle.
The Gujarat verdict that showed that PM Modi "is not all that invincible," said Mr Mukhopadhyay.
Justice OP Saini said Thursday that investigators could not prove that Mr Raja along with some officials from companies that won the licenses for telecom services had conspired to receive kickbacks from the sale of phone permits, causing a loss to the government. Reliance ADA Group officials -- Gautam Doshi, Hari Nair and Surendra Pipara -- and two promoters of D B Realty Ltd., Shahid Balwa and Vinod Goenka were also let off by the court. The charges against Essar Group promoters, Anshuman and Ravi Ruia, were also scrapped.
"This is a huge setback for BJP's anti-corruption plank," said Arati Jerath, a New Delhi-based author and political analyst. "They have lost a major political weapon and now have to re-strategize for 2019."
There was a "huge bit of arbitrariness" in the allocation of 2G airwaves leading to a revenue loss to the government, Finance Minister Arun Jaitley said after the verdict. He added investigating agencies will decide on further course of action in the matter.
The court ruled "the spectrum sale was a notional loss and not a scam," said Mohan Guruswamy, chairman at New Delhi-based Centre for Policy Alternatives and an adviser in the previous BJP government. "It's doubtful if the government will go for strong appeal against the judgment. Politicians don't like to prosecute possible future allies or corporates."
The telecom scandal led India's top court to cancel 122 licenses sold to companies, including the local joint ventures of Norway's Telenor ASA, UAE's Etisalat and Russia's AFK Sistema.
Shares of companies whose officials were acquitted surged after the court verdict. Unitech jumped 12.77 percent at 3:16 p.m. in Mumbai, Reliance Communications was up 3.82 percent while D B Realty surged 19.94 percent. The S&P BSE Sensex and NSE Nifty 50 Index were little changed.