"It seems to have been related to today's date," Jorge Gomez, a human rights official in the town of Barrancabermeja, Santander Province, where the murders took place, told reporters.
Tuesday's date was June 6, 2006, or 6-6-6, a set of numbers taken by some to be the mark of the devil. Police said that, plus the fact that there were six victims, raised their suspicion that there could be a ritualistic angle to the crime.
Three family members in the house at the time of the attack were being questioned by police and a suspect not related to the victims has been detained, authorities said.
"These are demonic things. The devil did this," a neighbor of the family told local television.
For days Colombian media have been filled with stories about 6-6-6, and worries in this mostly Catholic country of 41 million people that the Antichrist could appear.
In chapter 13, verse 18 of the King James version of the Bible's Book of Revelations, 666 is the number of "the beast." The number has a long association in both occult literature and popular culture with Satan, the fallen angel in Christian doctrine also known as "the devil," Lucifer and "the beast."