A drive-by shooting at a mini-mart in the south Medellin suburb of San Pablo Monday night left four people dead.
Unknown assassins in a gray car opened fire on the small grocery store with 45 caliber pistol, killing the four men inside.
Police ruled out the suggestion that the attack was an attempted robbery and said it may have been the work of a gang, El Colombiano reported.
A neighbor said the incident was unusual and that there had not been any murders in the area for some months.
Police are also investigating a double murder that occurred on a football field in the neighborhood of Ajizal.
They say the have a 23 year old man in custody who was caught attempting to escape the scene.
Medellin has been plagued with an increase of homicides for months.
The capital of Antioquia has been promised 30 billion pesos (US$15 million) from Colombia's national authorities to improve the security situation.
Between January and April this year, 512 people were assassinated in Medellin. This was a 66 percent rise compared to the same period last year.
