SÃO PAULO, Brazil — The sun had just begun to rise here one morning in September as André Peres de Carvalho, an officer in a special-operations police squad, prepared to leave his home. Two masked gunmen lurking outside the door did their work quickly, killing him before disappearing by motorcycle into the crazy quilt of São Paulo’s sprawl.

He was one of more than 70 police officers killed this year in São Paulo, Brazil’s largest and most powerful state. The sharp increase in murders of police officers, up almost 40 percent since last year, has raised fears of a resurgence of the First Capital Command, a criminal organization that carried out a harrowing four-day uprising here in 2006 during which almost 200 people were killed.

São Paulo officials have tried to play down the suspected role of the criminal group in this year’s police killings, calling it a violent reaction by a variety of criminals to tougher policing strategies. But security analysts and some members of São Paulo’s own state police force have characterized the killings as deliberate reprisals by the gang, commonly referred to as the P.C.C., or Primeiro Comando da Capital in Portuguese.

“We’re witnessing a low-intensity war unfold between police units and Brazil’s most powerful criminal organization,” said Camila Nunes Dias, a sociologist who specializes in the P.C.C. at the University of São Paulo’s Center for Violence Studies. “The retaliatory nature of this conflict shows that it can endure for some time to come.”