A Brazilian man who gave evidence to a United Nations human rights commission visiting Brazil has been shot dead.
Asma Jahangir spent three weeks investigating in Brazil
Gerson Jesus Bispo was the second person to be killed after speaking to UN envoy Asma Jahangir about alleged death squads, murder and torture by police.
Human rights groups say the two men were killed in retribution for talking to the envoy, who has been outspoken about the situation in Brazil.
Some of the country's most senior judges have responded angrily to her suggestion that the United Nations should offer advice on reforming the country's legal system.
Mr Bispo, 26, was on his way to work when he was shot dead by gunmen on a motorbike on Thursday in the city of Santo
Antonio de Jesus, 1,400 kilometres (870 miles) northeast of
Sao Paulo in the state of Bahia.
The car mechanic had presented evidence to Mrs Jahangir about the murder of his brother last year. He said a death squad possibly linked to the police was responsible.
Sandra Carvalho of the Brazilian human rights group Global Justice Centre said: "Bispo was killed because of the information he had on the death squads active in the state of Bahia. He obtained this information, which he must have given Mrs Jahangir, while investigating his brother's death."
Nilmario Miranda, head of Brazil's federal human rights office, told reporters that Mr Bispo's death was "an open challenge" by the death squads "to demonstrate that they are untouchable".
Two weeks ago a 24-year-old, Flavio Manoel da Silva was shot dead in the state of Paraiba, also in the north-east of Brazil. Just days earlier he too had spoken about death squads to the UN envoy.
Mrs Jahangir spent three weeks in Brazil investigating summary executions and other killings allegedly carried out by police before concluding that some of the country's police force did continue to kill civilians with impunity.
During her meeting with President Luiz Inacio Lula da Silva she suggested the UN could offer recommendations to help reform Brazil's legal system.
The president responded favourably but some judges view the idea as unconstitutional.
One said that agreeing to an external inspection would put Brazil in the same position as Iraq.
He said the country would be then a republic subjected to international control.
Mrs Jahangir is now preparing a report on her visit.