Pravin, 28, was arrested from Pune on Sunday evening.
The police in Maharashtra have arrested a third suspect in the murder of former minister Baba Siddique, who was shot dead in Bandra on Saturday.
Two of three suspected shooters had been arrested after the firing on Saturday night and, on Sunday, there was a post on Facebook from the handle of one Shubuu Lonkar, believed to be that of Lawrence Bishnoi gang associate Shubham Rameshwar Lonkar, claiming responsibility for the killing. While Lonkar is in jail, police said the post was made by his brother, Pravin Lonkar.
Pravin, 28, was arrested from Pune on Sunday evening. Officials from the Mumbai Police said that, apart from writing the post, in which a warning had also been issued to those who "help Salman Khan", he was a conspirator in the killing.
Pravin and Shubham, officials said, were the ones who had enlisted two of the shooters, Dharmaraj Kashyap and Shiv Kumar Gautam, in the plot. While Gautam is on the run, Kashyap was arrested on Saturday and he claimed in a court in Mumbai on Sunday that he is a minor. Since his Aadhaar card states that he is 19, the court has ordered a bone ossification test to ascertain his real age.
In the post, Pravin had written that Siddique had been murdered because he was linked to India's most wanted terrorist Dawood Ibrahim, was close to Salman Khan and because of the death of Anuj Thapan, one of the arrested suspects in the shooting outside Mr Khan's house in April, in police custody.
"We do not have any enmity with anyone but whoever helps Salman Khan and the Dawood gang, keep your accounts in order ('hisaab-kitaab kar lena')," he wrote in Hindi
The police are now on the lookout for Shiv Kumar Gautam, a resident of Uttar Pradesh, and the alleged handler of the three shooters, Mohammad Zeeshan Akhtar, who is believed to be hiding in Mumbai.
The Bishnoi gang has said it wants to kill Salman Khan because of his alleged involvement in shooting blackbucks at Bawad in Mathania near Jodhpur in September 1998, during the filming of 'Hum Saath Saath Hain'. The alleged act had upset the Bishnoi community, which considers the blackbuck sacred.