A retired Brazilian colonel who last month admitted carrying out torture during the country's 1964-1985 military rule has been found dead following a break-in at his suburban Rio home, police have said.

Paulo Malhaes, 76, was believed to have been killed after three men broke into the family property in the northern suburb of Novo Iguacu on Thursday, his widow told police on Friday.

"An evaluation of the scene has already been undertaken and the wife of the victim and their valet have been questioned. The latter will be able to help produce a photofit," a police spokesman told the AFP news agency.

Police said the men held the couple and the valet in separate rooms on Thursday night before killing the colonel and escaping with a number of firearms he collected.

However, media reports on Saturday indicated that the coroners were not ruling out the cause of death being a heart attack. Police were still investigating the claims that three men robbed the house at the time of death.

Graphic testimony 

Last month, Malhaes gave graphic testimony to Brazil's Truth Commission, established by President Dilma Rousseff into crimes committed during military rule.

He became the first former officer openly to admit to carrying out torture at a secret location dubbed the 'House of Death' at Petropolis outside Rio.

Malhaes testified to having mutilated some victims' bodies, cutting off their fingers and removing their teeth to prevent identification.

He also gave information about a military operation to dispose of the remains of slain poltician Rubens Paiva in 1971.

Brazil's then military leaders passed an amnesty in 1979 for political crimes committed during military rule but in 2012 Rousseff, who herself suffered torture as a former leftist activist, launched the Truth Commission which is due to present its conclusions in December.

The Military Club, an association of retired military-rule members, said it would not comment until it knew the circumstances of Malhaes' death.

Unlike Argentina, Chile and Uruguay, Brazil has yet to hold trials for military-era crimes and its Truth Commission has been only timidly addressing a period which officially saw 400 opponents killed and many more disappear with an estimated 20,000 suffering torture, AFP reported.

That compares with some 30,000 deaths in Argentina and more than 3,000 in Chile.