BOGOTA, COLOMBIA, AUG. 13 -- Gunmen shot dead an ex-congressman and a former judge in separate attacks today in what could signal the start of a new round of drug-related violence in Colombia after police killed a top drug baron on Saturday.

Gunmen firing from a car shot dead political leader and former congressman Eusebio Munoz Perea, a member of the ruling Liberal Party, as he drove through Cali, headquarters of Colombia's second-biggest cocaine cartel about 190 miles southwest of this capital.

The killers lobbed a hand grenade at policemen who chased them through Cali streets, but no one was injured. Police said they later arrested three suspects.

Carlos Campo, a former judge of the high court for Colombia's Atlantic coastal region, died after being shot three times in the head by assassins riding a motorcycle in the Caribbean coastal town of Barranquilla, police said.

In another attack, a small bomb exploded in Bogota's Model Prison, causing damage but no injuries. Police believe prisoners could have been trying to escape.

It was unclear if the sudden rise in violence was linked to the police killing in Medellin Saturday of Gustavo Gaviria, second-ranking leader of the Medellin cartel and cousin of drug lord Pablo Escobar. The traffickers often have attacked politicians and judges during a bloody year-long war on the state.

Colombia has been relatively quiet since the drug barons declared a unilateral truce July 27. But authorities fear the killing of Gaviria could spark new violence. He was killed less than a week after new President Cesar Gaviria (no relation to Gustavo) took office, pledging to make the anti-drug fight more effective.

A police spokesman in Medellin said police and army units in the city had been put on maximum alert. Residents of Medellin, 160 miles northwest of Bogota, said the city was tense, with people bracing for a response from the traffickers for Gustavo Gaviria's death.

A government source said the authorities believed Gustavo Gaviria was responsible for directing many attacks in the drug war. "If anything could contribute to reducing terrorism, it was the death of Gaviria," he said.