Venezuela's security forces have arrested two former police officers in connection with the killing last week of state prosecutor Danilo Anderson.
The killing shocked many Chavez supporters
Interior Minister Jesse Chacon said brothers Rolando and Otoniel Guevara were arrested in Carabobo state, west of the capital Caracas, on Friday.
A National Guard official said their homes and offices were being searched.
Earlier this week two people suspected of involvement in the murder were killed in shootouts with police.
Attorney Antonio Lopez was shot dead after he apparently opened fire on officers in Caracas on Tuesday, AP news agency reported.
And a man identified as Juan Carlos Sanchez was killed by police on Thursday in his motel room in the town of Barquisimeto.
Officials gave no details about the alleged role of the Guevara brothers in Danilo Anderson's killing.
Mr Anderson was investigating an attempt to overthrow President Hugo Chavez two years ago when he died in a car bomb attack on 18 November.
The killing sparked protests in Caracas.
Government and opposition condemned the attack, which has sparked fears of a return to violence in the deeply polarised country.
Mr Anderson had been preparing a case against about 400 opposition members, including politicians, lawyers and businessmen, accused of supporting a short-lived coup against Mr Chavez in 2002.
The prosecutor said recently he hoped to be able to file indictments soon.
But correspondents say Mr Anderson had been castigated by opposition members as being the instrument of Mr Chavez's political revenge on his opponents.