Boca Raton police officer Sandra Boonenberg said Monday the investigation was reopened several weeks ago based on new information stemming from Rodriguez's lawsuit against MLB.
Boonenberg offered few details on the open investigation but said detectives have "a lot of leads that they're pursuing."
The documents were stolen in March from the car of Porter Fischer, who took them from Biogenesis of America, the now-closed Florida anti-aging clinic where he worked.
The clinic and its owner, Anthony Bosch, have been accused of providing banned performance-enhancing drugs to Rodriguez and other major leaguers. Bosch agreed to co-operate with baseball's investigators, and baseball Commissioner Bud Selig on Aug. 5 suspended the New York Yankees third baseman for 211 games for alleged violations of the sport's drug agreement and labour contract. The players' association filed a grievance in an attempt to overturn the penalty.
ESPN, citing unidentified sources close to the investigation, reported last week that MLB impeded the Florida investigation.
"MLB investigators knowingly purchased stolen documents in their quest to allow Commissioner Selig to act, for the first time, as if he was tough on PED use in baseball despite striking a co-operation deal with Anthony Bosch who MLB knows is under federal investigation for providing steroids to minors," Jordan Siev, one of Rodriguez's lawyers, said in a statement.
MLB has repeatedly denied the accusation.
"The truth continues to be that we did not knowingly purchase stolen documents and there is an active police investigation to determine if the documents were in fact stolen," the commissioner's office said in a statement.