[1] Considered by analysts as one of the most powerful political figures in Alan García's first administration, he served as Deputy Minister and subsequently as Minister of the Interior during the most tense years of the Peruvian internal conflict between the Peruvian government and the terrorist organizations, the Shining Path and the Túpac Amaru Revolutionary Movement.

[3] He was sentenced to six years in prison based on charges of corruption as he was caught on videotape receiving bribes in one of Vladimiro Montesinos secret video recordings at the National Intelligence Service headquarters, in exchange for the Peruvian Aprista Party's support of President Alberto Fujimori's administration in 2000.

During his tenure as Minister of the Interior, he was accused of leading the supposed paramilitary command "Rodrigo Franco", with the task of eliminating suspected terrorists.

In 1992, upon Alan García's request for political asylum granted by the Colombian government, Mantilla was chosen as his successor as Secretary General of the party, in December 1992.

Following his congressional tenure and the 2000 general election, it was revealed to the media that Mantilla received $30,000 USD from presidential advisor and Intelligence Chief Vladimiro Montesinos on March 13, 2000, destined for party funds in exchange for political support of Alberto Fujimori's regime.