The five men are based out of Goa and Maharashtra adjoining the Karnataka border, an SIT official said, adding they had taken part in the crimes.
As the SIT started cracking the murder of Lankesh, a journalist-activist with strong anti-Hindutva views, leading to the arrest of key players in the killing of rationalists Narendra Dabholkar and MM Kalburgi, it discovered the wide network of operatives of the gang involved in these incidents.
"The leadership of Goa-headquartered Sanatan Sanstha was aware of the activities of its footsoldiers and lower rung cadre. We cannot subscribe to this statement that the leadership was not aware of it. They definitely knew about these plots," the official claimed.
He, however, said it was "tricky" to say the outfit had morphed into a terrorist organisation.
The official, however, said there were sufficient reasons to invoke the stringent Karnataka Control of Organised Crime Act against the gang members. KCOCA is the Karnataka version of MCOCA, the law in place in Maharashtra to curb underworld activities, often dubbed as draconian by civil rights groups.
Several people with alleged links to the Sanstha have been arrested in connection with these killings, but the outfit has insisted they were not its members.
Sanatan Sanstha spokesman Chetan Rajhans recently said some people with so-called "progressive mindset" and political parties like the Congress and the Left bloc were trying to put the organisation in the dock without providing evidence of any wrongdoing.
Karnataka Deputy Chief Minister G Parameshwara had said on Tuesday the state police was yet to establish the role of Sanatan Sanstha in the killing of Lankesh.
Lankesh, an outspoken critic of pro-Hindutva ideology, was shot dead outside her residence here on September 5 last year.