(Adds source pointing to sunken tanker, oil possibly Venezuelan)
By Rodrigo Viga Gaier and Gabriel Ponte
RIO DE JANEIRO/BRASILIA, Oct 8 (Reuters) - Brazilian President Jair Bolsonaro said on Tuesday that mysterious oil slicks polluting northeastern beaches likely had criminal origins, without explaining further.
Bolsonaro also appeared to row back comments from Monday, when he suggested the oil could be from a shipwrecked vessel, suggesting the evidence did not suggest such a cause. He also said he did not want to blame another country without proof, or it would cause a problem.
"If it was a shipwreck, oil would still be coming up. It is more probable that something was dumped there criminally," Bolsonaro told reporters.
A study by state-run oil company Petroleo Brasileiro SA , or Petrobras, suggests the oil came from Venezuela, according to a person familiar with the matter, who suggested that the volume of oil pointed to a sunken oil tanker.
Petrobras said that molecular tests on the organic material in samples of the crude oil showed they were not compatible with the oils it produced and sold. The company declined to say whether the oil slicks were from Venezuelan crude.
The oil has washed up in recent weeks on more than 100 beaches in nine northeastern states from Maranhao to Bahia. Its origin has generated an array of speculative explanations amid growing environmental concern.
"It does not look like a criminal spill. It seems to be accidental," said the person familiar with the Petrobras study, who requested anonymity because the report is not public.
Speaking with lawmakers on Tuesday, Petrobras Chief Executive Roberto Castello Branco said the company had collected 133 tonnes (146.6 tons) of oil along Brazil's northeastern shoreline, adding the slicks were "strange" and "worrying."
In an emailed statement, Petrobras said the company's environmental crews had worked on the cleanup of beaches in eight states in recent days at the request of Brazil's environmental protection agency, Ibama. (Reporting by Rodrigo Viga Gaier in Rio de Janeiro and Gabriel Ponte in Brasilia; Editing by Richard Chang and Peter Cooney)