this , but basically Colosio was groomed to be Salinas succesor by him (which was normal since they were both liberals), the problem happen when Colosio wanted to fired Ernesto Zedillo (who was a salinas puppet) from his proposed cabinet, killing any influence Salinas had in his cabinet,

Also Colosio wanted to work with Cuauhtémoc Cárdenas son of socialist president Lazaro Cardenas, and leader and founder of the PRD a leftist party at the time, who Salinas hated with all his soul, so Colosio betrayed Salinas the moment the won the candidacy, plus his killer was the sole mastermind according to the police that Salinas controled back then, Colosio being killed by Salinas its not something hard to believe in Mexico, Salinas stoled tax money and founded a company with it, he started the mini-civil war in chiapas with the ELZN and sold the country to american interests, him killing an opponent its not out of character for him

if you want to learn more about the assasination, the netflix documental Historia de un crimen: Colosio is good i heard, idk if its in US netflix tho