Story highlights Prosecutors began the task of trying to establish a "quid pro quo" between Sen. Menendez and Dr. Melgen

The trial ended its fourth week

Newark, New Jersey (CNN) An official at US Customs and Border Protection told jurors at Sen. Bob Menendez's federal bribery trial Thursday that she received a "somewhat odd" request from the New Jersey Democrat's staffer on January 11, 2013, asking the agency to hold off delivering cargo scanning equipment to the Dominican Republic.

The request itself was "unusual" the official said, but the jury also learned that one day earlier, Menendez had been golfing in West Palm Beach with Dr. Salomon Melgen -- the person who stood to benefit financially from the delay, according to testimony and exhibits presented in court.

As the fourth week of the high-profile corruption trial came to a close Thursday, prosecutors began the task of trying to establish a "quid pro quo" between the two men by directly tying the political favors Menendez did for Melgen with the benefits the senator allegedly received in return. The men deny any wrongdoing.

Jurors heard testimony earlier this week that Melgen had acquired a lucrative contract with the government in the Dominican Republic for screening cargo at the island's ports, but the agreement had turned sour. Menendez later sought out assistance from a high-ranking official at the State Department in May 2012 to help resolve the contractual dispute and threatened to hold a congressional hearing if the issue wasn't resolved, according to testimony from the former deputy assistant secretary at the State Department's Bureau of International Narcotics and Law Enforcement.

Todd Robinson, a long-time diplomat and recent US ambassador to Guatemala, explained to jurors that lawmakers often make inquiries about American companies' business disputes in foreign countries, but "none" he knew of carried the threat of a hearing.

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