On his day-long visit to the state, the Gujarat chief minister arrived in Kochi and addressed a meeting of the Kerala Pulaya Maha Sabha.
He then flew down to the capital city to launch the Bharatiya Janata Party's poll campaign.
On the murder of leader T.P. Chandrasekheran, Modi said the Left Front and the Congress were engaged in "shadow boxing".
"(Chandrasekheran's widow) K.K. Rema's recent indefinite fast clearly showed that there exists a nexus between the Left and the ruling Congress here," Modi said.
"This very same nexus was seen during the probe into the murder of (BJP activist) K.T. Jayakrishnan and also in the Marad (massacre) case. Instead of bringing the accused before the law, the rival fronts are engaged in shadow boxing," he said to thunderous applause from the huge crowd here.
Modi, who spoke mostly in Hindi, assured his party supporters that when the BJP takes power in Delhi, there would be representation for Kerala.
Incidentally, the BJP is yet to open its account in the 140-member Kerala assembly and in the 20 seats from the state in the Lok Sabha.
Modi returned to Gujarat late in the night.