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The motive appears to have been robbery.
According to this Spanish-language report, Perez was killed in his home during a robbery attempt. Here's the somewhat-fractured English provided by a Google Translate of that link:
The former star Major League roper Pascual Perez, part of the trilogy Nigua Perez was killed in a robbery attempt at his home, according to the coordinator of the Department of Murder in the city of San Cristobal, Julio Ernesto Germosén.
The versions collected indicate that the pitcher received yesterday your pension money as professional baseball player, what would have motivated the criminals act against him.
Well, you get the idea. Perez was one of three brothers (Carlos and Melido the others) who pitched in the major leagues in the 1980s and 1990s and was perhaps best-known for getting lost one day on I-285 trying to find his way to Fulton County Stadium in Atlanta. He posted a 67-68 record with a 3.44 ERA in 207 appearances (193 starts) in an 11-year career.
Pascual Perez was 55 years old.