Valbuena and Castillo were killed on Thursday in a auto crash in Venezuela when the players' vehicle veered off a road.
The Orange County Register says the vehicle they were in reportedly hit a rock on the road in the state of Yarucuy. Julio León Heredia, the governor of Yaracuy in Venezuela, said the four suspects arrested by police were found with Valbuena's and Castillo's personal belongings.
He played with the Pittsburgh Pirates, the San Fransico Giants and the Houston Astros.
The Cardenales de Lara, the team Valbuena and Castillo were playing for, called the accident a "horrible tragedy", in a statement. His final season in Major League Baseball was with the Astros. He recorded a.254 batting average, 39 homes runs and 218 career RBIs.
"We are deeply saddened to hear of the passing of former Angel Luis Valbuena and former Major League Baseball infielder José Castillo", the Angels tweeted. He also played for the Mariners, Indians, Cubs and Astros during an 11-year career that began in 2008.
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"I will miss Luis's banter, smile, genuine love for his teammates, and, of course, the bat flips", Astros manager AJ Hinch said in a statement. Off the field, he was a warm and friendly presence to all who interacted with him.
Major League Baseball players Luis Valbuena and Jose Castillo have been killed in a vehicle crash in Venezuela.
Castillo, 37, joined Major League Baseball in 2004.
CubsHQ.com would like to send our most heartfelt condolences and prayers to the family and friends of Luis Valbuena and Jose Castillo.