Robert Serra and Maria Herrera were stabbed to death in Caracas.
Mr Maduro said Mr Serra’s bodyguard had confessed to conspiring with a Colombian gang to kill the member of the National Assembly.
The president also said that there had been a series of attempts to kill other top socialist party officials.
Mr Maduro had previously blamed “ultra-right” opposition groups in Venezuela and in neighbouring Colombia for the murder.
At 27, Robert Serra was one of the youngest members of the National Assembly
In a news conference on Wednesday he gave more details of the evidence he said had emerged since.
He played an out-of-focus video of a man apparently confessing to the murder. In it, the man said that he was convinced by someone he refers to as “the Colombian” to “get rid” of Mr Serra.
A surveillance video showed four men entering the home of Mr Serra, while two other suspects were said to be waiting in getaway cars.
Two suspects, one of them Mr Serra’s bodyguard, have so far been arrested and the president said he would “get to the masterminds of Serra’s murder inside or outside of the country”.
He said that in the days after Mr Serra’s murder there had also been attempts on the lives of the president of the National Assembly, Diosdado Cabello, and that of the education minister, Hector Rodriguez.
Of the unnamed paramilitary group he has blamed for the attacks he said: “Their motivation, their inspiration, their preparation, their funding aims to destabilise the country and it is part of a series of crimes that they have planned and we have managed to foil them in time.”
However, he did not give any further details of the alleged attempted attacks on Mr Cabello and Mr Rodriguez.
Critics of Mr Maduro have accused him of exaggerating the threats in order to justify the arrest of opposition activists.