ASUNCION (AFP) -- Authorities exonerated a man of blame after he shot dead a robber who threatened his 12-year-old son by forcing his handgun barrel into the boy's mouth, press reports said here.

Carlos Nunez, 52, was leaving his house with his wife and three children early Thursday when they were confronted by Edgar Vergara, 22, an ex-convict who had just committed a robbery, according to the reports Friday.

Vergara seized Nunez's son, placed the barrel of a pistol in his mouth and demanded valuables.

The family handed over two cellular phones and about 35 dollars, whereupon Vergara fled on a city bus.

Nunez went in his house, got his shotgun, and with the help of neighbors followed and intercepted the bus with his car.

When Vergara got off the bus, Nunez took aim from his car and shot Vergara in the head, said the reports.

Prosecutors found Nunez had acted in self- defense and released him.