After allegedly receiving threats, Jain, who lives in Gulf, deleted the controversial post from his Facebook account.
On Tuesday, he had reportedly posted, "I have been waiting to hear this good news for a long time. Salutations, dear comrades. Feeling excited."
In his later posts, Jain had 'defended' his post saying that "14 years ago, Manoj was involved in an attack on his father".
Even though, he deleted the post, but many people have taken its screen-shot, that has gone viral.
Meanwhile, the state BJP president V Muraleedharan condemned the incident and said, "A person who wrote a Facebook post on a murder should be booked. It shows that he could have a role in the murder plan. It is abominable to congratulate killers."
On Monday, country-made bombs were hurled at the car in which Manoj and his companions were travelling and the attackers then hacked him to death.
On Tuesday, RSS-BJP leaders alleged that the CPI(M) was behind the killing and gave a call for a dawn-to-dusk hartal in the state.
Home Minister Rajnath Singh also asked Kerala Chief Minister Oommen Chandy to take strict action to stop political killings in the state.