Regional director Reynaldo Esmeralda, chief of the NBI-Special Task Force, said he received a one-page letter from Sanchez requesting for the parallel probe.
With a solution "yet forthcoming," Sanchez said he believes that the NBI "could help in solving this dastardly crime."
Esmeralda said Sanchez sought their help after Senior Superintendent Ricardo Padilla, who once headed the special task force probing the explosion, has been transferred as director of the Southern Police District in Metro Manila.
"Up to now, there has been no resolution to the case," he said.
The June 1 blast killed Sanchezs driver, Luisito Icaro, and police bodyguard, PO2 Eric Landicho. The governor sustained second-degree burns.
Police said they found pieces of a deformed plastic bottle cap, a copper coil and wire, which tested positive for TNT.