Federal police say the Suezmax Bouboulina docked in Venezuela on 15 July before heading to Singapore with a stop in South Africa. Brazilians authorities have previously identified the heavy crude as Venezuelan.
Two sources in Venezuela, one from state-owned PdV and the other from the oil union, say the tanker loaded 16°API Merey blend in mid-July on behalf of Rosneft, the Russian company that has emerged as the main lifter of Venezuelan crude since the US imposed oil sanctions on Caracas in late January.
Police carried out search warrants today at the Rio offices of the shipowner, which freight records indicate is Delta Tankers.
"From the location of the initial spot, which is suspected to have occurred between July 28 and 29, it was possible to identify the only oil tanker that sailed through the suspect area using geo-intelligence techniques and regressive oceanographic calculations," federal police said in a note.
Brazil's navy said of the 30 vessels it was investigating, only a Greek-flagged one was navigating in the spot carrying crude from Venezuela's Jose oil terminal to South Africa.
Ship tracking data shows the Bouboulina was off the Brazilian coast near Recife at the point when the spill occurred. Athens-based Delta Tankers, owner of 30 crude oil tankers including the Bouboulina, declined to immediately comment.
Venezuela has denied any responsibility.
In its statement issued this morning, the police added that "Investigations continue to identify the circumstances and factors involved in this spill (whether accidental or intentional), the dimensions of the original oil slick, as well as to measure the volume of oil spilled, to estimate the likelihood of residual stains, and to ratify the spill pattern."
Earlier this week, Roberto Castello Branco, chief executive of state-controlled Petrobras, said the spill was the biggest environmental "attack" Brazil had ever experienced. His statement echoed earlier comments from Brazilian president Jair Bolsonaro, who has hinted the spill may have been a criminal act aimed at disrupting a giant 6 November auction of pre-salt reserves in the offshore area known as the Transfer of Rights (TOR).
Petrobras denies any involvement in the spill, but has participated in clean-up efforts and analysis.