BJP leader Amit Shah speaks during a news conference in Lucknow on March 1, 2014.
Amit Shah is charged with three counts of murder. He is also a key election campaign manager and close aide of Narendra Modi, the BJP's candidate for prime minister.
To supporters, Mr Shah's proven talent in winning elections makes him the obvious choice to run Mr Modi's campaign in Uttar Pradesh, a swing state that holds the key to national power.
But critics say Mr Modi's ties to Mr Shah are proof of a dark side to the Hindu nationalist leader who is storming ahead in opinion polls.
"This man faces criminal charges. But if Modi wins, he could be one of India's most powerful politicians," said Mukul Sinha, a lawyer representing relatives of victims in the cases against Mr Shah, commenting on his appointment as campaign manager for the BJP in Uttar Pradesh.
A stocky, bearded figure and son of a well-to-do businessman, Mr Shah, 50, was Home Minister of Gujarat for seven years before his 2010 arrest and subsequent release on bail.
Mr Shah denies charges that he ordered the killing of Sohrabuddin Sheikh, a petty criminal who was shot dead by the Gujarat police in 2005. The police alleged that he was a terrorist who planned to assassinate Mr Modi. Officers snatched Mr Sheikh from a bus with his wife, then allegedly staged a gunbattle. Mr Sheikh was killed and his wife's cremated body was found in the village of one of the policemen. A witness traveling with them on the bus was killed later.
The CBI, assigned to investigate the case, has said in its charge-sheet that the encounter was staged.
According to the CBI's charge-sheet, phone records show Mr Shah, as Home Minister, had multiple calls with the accused officers during the operation that culminated in Mr Sheikh's killing.
The BJP says the Central Bureau of Investigation's (CBI) charges were influenced by the Congress-led government, which is often accused of using the federal agency to harass enemies.
"This is a politically-motivated campaign," said BJP spokeswoman Meenakshi Lekhi.
Mr Shah and his lawyers did not respond to requests from Reuters for an interview, but last year he said the case was a political vendetta.
"All of this is being done to defame Chief Minister Modi, me and the BJP," he told a private news channel, arguing that similar killings elsewhere in India were not subject to probes.
Mr Shah has much in common with his mentor.
Both joined the Rashtriya Swayamsevak Sangh (RSS), the voluntary right-wing group that serves as the ideological incubator for Hindu nationalism and as the philosophical parent of the BJP.
"Amit Shah is a misunderstood man. There have been no riots in Gujarat for 12 years," said Lalji Tandon, a BJP lawmaker in Uttar Pradesh. "He's doing a good job in this state at mobilising the grass roots. He's a top organiser, from everything down to the polling booth."
After resigning from the Gujarat state cabinet following his arrest, Mr Shah kept a low profile until being named to lead the Uttar Pradesh campaign. But critics accuse him of adding to religious tensions in the state.
Soon after arriving there last year, Mr Shah visited the site of the Babri Masjid, the 16th/17th-centruy mosque razed by Hindu fundamentalists in 1992, and said a Hindu temple should be built there.The destruction of the mosque led to nationwide riots that killed nearly 2,000.
The BJP says the mosque stood on a holy Hindu site.
Mr Shah last year clarified the dispute over the religious site was not an election campaign issue.
Nevertheless, when Hindu-Muslim violence broke out in Uttar Pradesh's Muzaffarnagar district shortly after Mr Shah's arrival, the union government was quick to make the connection, with minority affairs Minister Rahman Khan telling a magazine that Mr Shah had been sent by the BJP expressly to stir up communal tension.
No evidence has been produced to back that charge and villagers in Muzaffarnagar district, where the clashes erupted, say local politicians from several parties fomented the violence in which more than 40 people died. Police have charged two BJP legislators and politicians from other parties with provoking violence via social media and making inflammatory speeches.
© Thomson Reuters 2014