Two police officers suspected in a shooting spree that left 30 people dead in Rio de Janeiro last week were detained Saturday after an intensive manhunt, authorities said.

State Gov. Rosinha Matheus (search) also offered a $1,900 reward for information leading to the capture of the gunmen.

"We want this case to be rigorously investigated because it can't go unpunished," Matheus said Saturday on her weekly radio program. "As a mother I'm shocked. Only monsters are capable of that."

Composite sketches and anonymous tips led police to officers Jose Augusto Moreira Felipe, 32, and Fabiano Goncalves Lopes, 30, police said. They were being interrogated but had not yet been charged, said Marcela Lobo, a spokeswoman for the Rio de Janeiro Public Safety Department.

The two officers, who worked in the district where the shootings occurred on Thursday, were taken into custody at their home, police said. A .380-caliber pistol and a motorcycle also were found, though authorities have not said if the weapon was used in the shootings.

Thursday's killings were the bloodiest massacre in years in a state already famous for its homicide rate. Authorities had suspected the killings were the work of rogue police angered by the arrest of eight other officers caught on film while disposing of two bodies.

The neighborhoods where the shootings took place are part of the Baixada Fluminense (search), a vast, drab sprawl of poor suburbs on Rio's north side. Elite units of the Rio state police, aided by federal agents, set up road blocks and searched houses in the area.

Police believe the suspects were linked to so-called death squads — shadowy associations, often made up of off-duty or retired police officers, hired by local businessmen to kill undesirables.

Marcelo Itagiba, Rio's state security secretary, said the crime was likely the work of police angered by the arrest of eight officers caught on film while disposing of two bodies.

But Justice Minister Marcio Thomaz Bastos (search) said it was too early to confirm that corrupt police carried out the killings.

"We must follow all lines of investigation so nobody gets away, whoever they may be," Bastos said.

According to witnesses, the shooting started around 10 p.m. Thursday when four men got out of a silver Volkswagen and opened fire on the crowd at a street-corner bar in Nova Iguacu (search). Fifteen people were found dead in and around the bar, and three more died in the hospital Friday.

The gunmen left the scene, firing randomly and killing two bicyclists along the road, then killed 10 people more in Queimados (search), a neighboring town.

Victims were buried Saturday, as families wept and held up banners calling for justice. A memorial mass for the victims was planned late Saturday at the Santo Antonio Cathedral in Nova Iguacu.

Nova Iguacu Mayor Lindberg Farias said death squads were nothing new in his city, one of the poorest in the region.

"Everybody knows that deaths squads operate in the Baixada, including the names of those who are linked to death squads," said Farias in an interview on CBN radio.

Earlier this year, a death squad was blamed for killing a family of four in Nova Iguacu after one of the sons was accused of stealing a bicycle.

"What alarms me most is the point to which Rio de Janeiro has sunk. Besides shootouts between bandits, and the drug war, we are now seeing a battle [pitting] police against police where the only losers, really , are the people," Farias said.

The homicide rate across Rio de Janeiro state is among the highest in the world at around 50 per 100,000 residents. In the Baixada, it climbs to 76 per 100,000.

Police death squads in Brazil caused an international uproar 12 years ago, when eight street children were killed as they slept outside a church in downtown Rio.