Brazil's solicitor general said the country would seek damages in the case, which has hurt tourism and fishing communities in the poorer northeast region.
Brazilian investigators claimed on Friday a Greek-flagged ship carrying Venezuelan crude was the source of oil tarring Brazil's coastline over the past two months, but the firm running the ship denied this, saying its voyage finished "uneventfully."
A federal police document seen by Reuters said the tanker, Bouboulina, owned by Greece's Delta Tankers Ltd, appears to have spilled the crude about 700 kilometers off Brazil's coast around July 28-29, after loading the oil at Venezuela's Jose terminal.
Delta Tankers said the Bouboulina had left Venezuela on July 19 bound for Melaka, Malaysia, "where she discharged her entire cargo without any shortage." In a statement, the company said the trip proceeded "uneventfully," adding that it would cooperate with the probe, "if contacted."
Since early September, tons of oil remains have reached the Brazilian beaches. The origin of this contamination, however, has not been officially determined.
Venezuelan authorities also denied last month that the foreign ship was carrying Venezuelan oil, while the state-owned company PDVSA stressed that no breakdowns or oil spills have been reported in its facilities, which are located about 6,650 kilometers away from the Brazilian coasts.
"There is strong evidence that the company, the captain and the vessel's crew failed to communicate to authorities about the release of the crude oil in the Atlantic Ocean," Brazilian prosecutors said in a statement.
Federal police also carried out searches at the Rio de Janeiro addresses of maritime services companies Lachmann and Witt O'Brien's, a subsidiary of Seacor Holdings Inc, according to a search warrant document seen by Reuters.
The police confirmed that they had raided two firms, without naming them. They said neither company was suspected of criminal activity, but said both had commercial relationships with the "Greek firm" in question.
Witt O'Brien's said the ship and operator under investigation had never been its clients in Brazil, adding that the activities of its Brazil office were unrelated to any kind of contract that could be relevant to the police inquiries.
Shipping agency Lachmann did not respond to a request for comment.
Brazilian authorities said they were seeking cooperation from international agencies, including Interpol, to further investigate the ship, its crew and the company.
Federal prosecutors said Brazil's navy also claimed to information regarding prior detention of the vessel in the United States for four days due to "incorrect operating procedures related to the separation of oil and water for release in the sea."
Prosecutors did not give details for when the alleged U.S. detention occurred, and Reuters was unable to verify the account.
The police said oceanographic and geolocation data showed that the Greek ship was the only one navigating near the origin of the spill between July 28 and 29.
From late August to the end of October, the oil washed ashore in nine states, according to federal police, closing hundreds of beaches and killing scores of animals. Volunteers trying to clean up the crude without proper equipment have also fallen sick.
Brazil has so far collected some 2,000 tonnes of sludge from its beaches in continuing cleanup efforts, while working to rehabilitate birds and sea turtles coated in the thick crude.
The slow and patchwork cleanup efforts, along with weeks of confusion about the cause of the spill, have spurred criticism of the government's response.
Because the heavy crude does not float on the ocean surface like most oil slicks, officials said traditional methods of tracking it and keeping it off the shore have been ineffective.
The latest report from the Brazilian Institute of Environment and Renewable Natural Resources (Ibama), released on Wednesday, says the crude oil has washed up on 283 beaches in 98 municipalities across nine states.
A total of 109 animals have been found with vestiges of crude oil, of which 28 of them were rescued alive and 81 died (mostly sea turtles).
In just the three northeastern states of Pernambuco, Alagoas and Bahia, which along with the state of Sergipe are under a state of emergency, a total of 3,792.6 tons of oil and sand were collected from contaminated beaches through Oct. 30.
It should be noted that this is not the first time that the Brazilian government and its agencies have tried to link Venezuela to the oil spill, failing to provide any kind of verifiable evidence for its claims.