Connecticut police declined to comment on the nature of Monday's search at Pine Lake in Bristol and referred calls to Massachusetts prosecutors. Gregg Miliote, a spokesman for the Bristol County district attorney, would not comment.
Hernandez has pleaded not guilty to murder in the death of Odin Lloyd, a 27-year-old Boston semi-professional football player whose body was found June 17 about a mile from Hernandez's home in North Attleborough, Mass. The ex-player's attorneys have called the case against him circumstantial.
Authorities believe Lloyd was killed with a .45-calibre Glock, which hasn't been recovered.
Police divers were in Pine Lake on Monday and other officers could be seen combing the water's edge.
Earlier this month, investigators executed several search warrants in Bristol at locations linked to Hernandez and his associates Ernest Wallace and Carlos Ortiz, whom authorities say were with Hernandez when Lloyd was killed.
They found a vehicle at the home of Hernandez's uncle that was wanted in a 2012 double killing in Boston. It had been rented in Hernandez's name
The warrants also were used to search an apartment linked to Ortiz and a rental car police say was used by Wallace and Ortiz to return to Connecticut after Lloyd's shooting.
Authorities have not said who fired the shots that killed Lloyd, but documents filed in Florida paint the former Patriot as the triggerman. According to the records, Ortiz told police that Wallace said Hernandez fired the shots.