Two police officers suspected in a shooting spree that killed 30 people last week were identified by witnesses who saw them at the crime scene, officials said Sunday.

Police officers Fabiano Goncalves Lopes (search) and Jose Augusto Moreira Felipe (search), who were arrested Saturday, were seen near the drive-by shootings that left 30 people dead on the city outskirts, officials said.

Police had arrest warrants for two other suspects who were linked to the crime by witnesses who saw their composite sketches, Justice Minister Marcio Thomaz Bastos said in Brasilia, the nation's capital.

Lopes, 30, and Felipe, 32, were on medical leave from the police department at the time of the killings, said Marcela Lobo, a spokeswoman for the Rio de Janeiro State Security Secretariat. Both had a history of disciplinary problems, she said.

Authorities believe the killings were a show of force by rogue police angered by the arrest of eight other officers caught on film while disposing of two bodies.

But many were perplexed by the seemingly random nature of the crime. Only two of the victims had criminal records and five were teenagers shot dead while playing video games at a local bar.

"If you want to show strength, you whack something with a stick, you don't kill innocent people," said Carlos Lima da Silva, whose brother Jonas, 19, was one of the victims.

Lobo said about 250 state police, aided by federal agents, continued to search Saturday for the other suspects across the Baixada Fluminense (search) — a vast sprawl of poor suburbs on Rio's north side where the shootings took place.

Another 400 to 600 federal officers were expected to arrive in Rio this week to reinforce the investigation and to increase security in the region, Bastos said after a meeting with Brazilian President Luiz Inacio Lula da Silva (search).

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.

Thursday's killings were the bloodiest massacre in years in a state already famous for its violence. The homicide rate across Rio de Janeiro state is among the highest in the world at around 50 per 100,000 residents, but in the Baixada, it climbs to 76 per 100,000.