"If you see the police doing something stupid, like violently attacking protesters, that could cause some very serious problems," Biundini said.
Security officials have said the stiffest security challenge will be providing security for the pope's two mass events on 2.5 mile-long (4 kilometer-long) Copacabana beach. Still, they insist they're experienced in handling mega-crowds and point to a string of concerts that have attracted similarly massive numbers of spectators to Copacabana.
April's bombing attacks on the Boston Marathon, which killed three and injured 264, have certainly raised sensitivities about the potential dangers of such mass events. But Brazilian police said there'll be no checkpoints or bag inspections of the crowds at Copacabana, similar to the security schemes at other events.
That doesn't mean the Brazilians won't be making a show of force.
Some 10,000 police officers and more than 14,000 soldiers will be on duty during the pope's visit, and six Brazilian military aircraft will provide transportation for the pontiff. The helicopters will let Francis avoid Rio's snarled traffic and the dangers of land travel.
Nearly 100 lookout towers will also allow police to monitor an expected 1.5 million people turning out for yet another mass event, the World Youth Day's closing Mass in the rural neighborhood of Guaratiba, about 30 miles (50 kilometers) west of Copacabana on the far outskirts of Rio.
Federal, state and local governments are expected to spend a total of around $52 million on all the security and logistical measures for the papal visit.
Even with such numbers, Francis' itinerary will at some points push him out of the reach of all but his immediate security detail, entrusting much of his protection to the crowd of faithful. Experts have warned that a lone wolf-style assailant presents the gravest security threat.
"Much of the pope's security will be provided by the Brazilian people" themselves, said General Presidential Secretary Gilberto Carvalho.