Troops fired tear gas in Venezuela's capital to disperse protesters demanding a crackdown on crime following the slayings of three young Canadian brothers, while the justice minister acknowledged police forces were in need of sweeping reforms.

Protests erupted in five parts of Caracas on Wednesday. In one of the demonstrations, hundreds gathered to block a highway near the affluent neighborhood of Altamira in eastern Caracas, a stronghold for opponents of President Hugo Chavez.

As the protesters were pushed back, some set tires and trash bins afire on nearby roads.

"Chavez always criticizes the United States and talks about thousands of innocent people killed in Iraq, but what about the thousands who are killed here," said protester Gustavo Marin, 26.

The unrest was touched off by the discovery Tuesday of the bodies of the three Faddoul brothers — John, 17, Kevin, 13, and Jason, 12, with dual Canadian-Venezuelan citizenship. The bodies of the boys, who were shot in the head and neck, were found outside Caracas more than a month after they were kidnapped at a bogus police checkpoint on their way to school.

The body of their 30-year-old driver was also found.

Justice Minister Jesse Chacon said every police force in the crime-ridden South American nation needed to be purged of corrupt cops. He urged Venezuelans to unite against violent crime, but not to turn the incident into a politically motivated attack against the Chavez government.

Attorney General Isaias Rodriguez said investigators have questioned two police officers in the killings, which drew widespread mourning and a sudden outburst of frustration at the constant anxiety Venezuelans feel over their security.

"Today it was them, but tomorrow it could be my sister and me," said Fady Rahal, a 16-year-old classmate of John, as she spoke through tears at a protest. "What kind of a country is this?"

A Venezuelan photographer died after being shot on his way to cover a protest Wednesday at the Central University of Venezuela. The photographer, Jorge Aguirre of the newspaper El Mundo, was approaching the university when an unidentified man on a motorcycle tried to stop his car, then shot him and fled, said Jose Gregorio Yepez, an editor at the paper.

Aguirre managed to take a picture of his killer's back as the man — wearing a blue jacket and helmet — rode away. Chacon said the photograph would help solve the crime.

Earlier Wednesday, some 400 demonstrators halted traffic at a different spot on the highway. As two police on a motorcycle approached, the crowd chanted "Respect!" and "We want justice!" while other police holding gas masks looked on from a distance.

About 200 protesters also gathered in front of the Justice Ministry in downtown Caracas, accusing authorities of failing to fight crime effectively. Dozens of cars and buses passing through downtown had "mourning" scrawled in white shoe polish across their windows.

Earlier, dozens of the boys' classmates — some with black ribbons tied on their wrists — shed tears after a Mass at their Catholic school.

The Venezuela-born brothers lived with their Canadian father and Venezuelan mother, both of Lebanese descent, in a gated community in an upscale Caracas neighborhood.

The boys were abducted Feb. 23 when unidentified men dressed as police stopped their car at a roadside checkpoint on their way to school. Officials said the kidnappers demanded more than $4.5 million — a ransom too steep for the parents to pay, their lawyer, Santiago Georges, said.

Two of the victims were still clad in their school uniform beige shirts, Federal Police Chief Marco Chavez said.

Violent robberies, kidnappings and murders are frequent in Venezuela, which has a population 25 million. There were 9,402 homicides reported in 2005, down slightly from 2004, according to government statistics.

Kidnappings also rose from 51 in 1995 to 201 in 2002, according to the latest government statistics available. Independent observers believe the real figures are much higher because many do not report kidnappings for fear of endangering their families.