"There are some (pieces) of information cropping up. There are five names, all with DA officer level 1, that are floating," he said.
"But we have to analyze this information because this is the gist of our investigation," he added.
Esperat, a hard-hitting columnist of Midland Review, was shot inside her home in Tacurong City, Sultan Kudarat last March 24.
Police have arrested four suspects, including the alleged gunman and lookout.
Gonzales said he has received a letter claiming that DA Central Mindanao director Sumail Sekkak, whom the National Bureau of Investigation earlier had tagged as the mastermind, had nothing to do with the killing.
He said he has turned over the letter to NBI director Reynaldo Wycoco to verify its authenticity, adding it may be intended to muddle the probe.
He said he is not convinced that Sekkak, whom Esperat had charged with graft, was behind the killing.
Wycoco earlier said Randy Grecia, the alleged lookout, had tagged Sekkak as the brains, saying that he (Sekkak) and his wife were dismissed from government service due to the charges filed by Esperat.
Gonzales, for his part, earlier linked a certain Osmena Montaner, a DA finance and budget officer in Central Mindanao, as the alleged mastermind.
He said a witness, who supposedly hired the four arrested suspects, identified Montaner in an extra-judicial confession to a Sultan Kudarat prosecutor.
"In other words, our witness had a better access to the mastermind than the lookout," he said, referring to Grecia, the police witness.
Gonzales said the DOJ had investigated Montaner for multiple murder for the burning of a hotel.
He said prosecutor Al Calica is looking into a different mastermind in the Esperat killing, said to be a DA budget officer and another employee ranked lower than Sekkak.