According to this report, it has been verified that the killers were looking for somebody who they thought was traveling in the same car as Diaz and his crew, which was not the case. According to Guatemalan police, the killers were looking for the person who contacted/invited Oscar to come to the race in Guatemala but he was not in the car with them.
The report says that when the criminals approached the car to verify if they had achieved their goal, they realized Oscar was not the person they were looking for and apologized and ran away.
Oscar's remains arrived today in Costa Rica, his home country, and the funeral will take place tomorrow morning. Godspeed, Oscar.