In the last decade, criminal activity has been greatly reduced, but not eliminated. In the last year, there have been 282 kidnappings, compared to 2,882 in 2002. But 282 is still a lot, and there are still many armed anti-social groups out there. The coalition of drug gangs and leftist rebels (mainly FARC and ELN) are being forced out of the country, or destroyed, by constant police and military action. Many of these guys are seeking new criminal activities that are not under so much pressure. Illegal gold mining is a favorite, as is smuggling and extortion. The criminal gangs go where the military and police presence is lightest. Too many men who spent some time as outlaws acquired bad habits they can never get rid of. Colombia is still a very violent place. It's not just that the police cannot suppress all of the violence; but that the courts often let criminals and killers go free (because of threats, bribes or overwork.)
Most of the violence is along the southern border and the eastern one with Venezuela. But people in "pacified" areas are demanding some attention be paid to all the bad guys that have gone from leftist rebellion and drug production to being local thugs.