Mr Karma and Mr Patel died in the ambush on Saturday evening. The 84-year-old Mr Shukla is in a critical condition in a Gurgaon hospital, with three bullet injuries in his abdomen.
The note, sent by a Maoist spokesperson from the Dandakaranya region in Chhattisgarh, says that a People's Liberation Guerrilla Army or PLGA detachment carried out the attack on the convoy of 25 cars carrying the Congress leaders.
Mr Patel, who was the chief of the Chhattisgarh Congress, was targeted because he approved Operation Green Hunt when he was the state's Home Minister, which allowed central forces to be a part of anti-Naxal operations, the note says.
Mahendra Karma, it says, was "punished" for what the Naxals called his "misdeeds". Mr Karma, also a former Home Minister, had in 2005 launched the Salwa Judum, an anti-Naxal movement that won him much praise from even the BJP's Raman Singh, who is the Chief Minister of Chhattisgarh.
In their note the Maoists have blamed Mr Singh's dispensation equally for what they call "anti-people policies". The note in fact criticizes Prime Minister Manmohan Singh, Congress president Sonia Gandhi and BJP chief Rajnath Singh too for calling Saturday's incident an attack on democracy. (There were security lapses in Chhattisgarh: Raman Singh)
They also have demands. Seven of them, mostly old demands. The Naxals want Operation Green Hunt to end and paramilitary forces to be sent back from Dandakaranya. They want laws like the Chhattisgarh Special Public Security Act 2005 (CSPSA) and the Unlawful Activities (Prevention) Act 1967 to be scrapped. They also want an unspecified number of their men and people they call "innocent tribals" to be released from jail unconditionally.
The note also demands that deals with corporates "that loot natural resources" be cancelled.