He then attended Brown University in Providence, Rhode Island, receiving an Artium Baccalaureus degree with a concentration in History in 1971.

In April, 1972, he graduated from the 23-week course of the United States Army Infantry Officer Candidate School in Fort Benning, Georgia, and was commissioned a Second Lieutenant in the Military Intelligence Branch.

After completing the Counterintelligence Officer and Personnel Security Adjudications courses at the United States Army Intelligence Center and School in Fort Huachuca, Arizona, he was posted to Detachment R, 500th Military Intelligence Group in Okinawa, Japan, where he served as Deputy Chief of the detachment's counterintelligence field office until 1974.

[1] After approving the Puerto Rico bar examination, he worked as an attorney in some of the leading law firms in San Juan, eventually becoming a partner.

While in private practice and as an Assistant United States Attorney, he litigated and tried all types of cases in the civil and commercial areas of the law.

Besosa was lead counsel or actively participated in various of the large complex litigation cases filed in the courts of Puerto Rico, including the E.I.

In 1994, he was a founding partner of the Adsuar, Muñiz, Goyco & Besosa, P.S.C., law firm and chaired its Litigation and Trial Practice Department and the Recruiting Committee.