In a motion filed Friday, Hernandez's lawyers argued that any evidence of so-called "bad acts" are not relevant to the murder charge against him in the 2013 killing of semi-professional football player Odin Lloyd. Hernandez's trial in that case is scheduled to begin next month in Fall River Superior Court.
Hernandez has pleaded not guilty to murder charges in all three killings.
Hernandez's lawyers said evidence about the double slaying in Boston in 2012 and other alleged crimes would risk "undue prejudice" against Hernandez in the Lloyd trial.
Prosecutors filed a notice in October listing 30 subjects of "potential other prior bad act evidence," including other shootings, gun trafficking, firearms possession, drug use and a drunken driving arrest, Hernandez's lawyers said in their filing.
"If permitted to use all, or even much, of this evidence, the commonwealth will have succeeded in transforming a murder trial into a wide-ranging, collateral attack on the defendant's personal history, character, lifestyle and propensities," Hernandez's lawyers wrote.
They argue that if evidence of the double slaying is presented at the Lloyd trial, it would "grossly undermine" Hernandez's right to a fair trial.
"It will be difficult enough for Hernandez to get a fair trial in this case without having to defend against two completely separate murder allegations (different time, different place, different weapon, different evidence) before the same jury simultaneously!" his lawyers wrote.
Hernandez's lawyers also want the judge to bar evidence about an incident outside a Providence nightclub in May 2013. Hernandez's lawyers said Hernandez was visiting the club with friends when they were "confronted, threatened and/or attacked by a larger, belligerent group."
As Hernandez and his friends went to their car, someone threw a handgun under a parked car. Hernandez's lawyers say the handgun was not the murder weapon in the Lloyd case and Hernandez was not the person who threw it.
"There is absolutely no factual connection between this incident and Odin Lloyd and his shooting death," his lawyers wrote.
Hernandez's defence team said they also object to prosecutors introducing any evidence of the shooting of Hernandez's friend, Alexander Bradley, in Florida in February 2013.
Bradley told police in Florida that he did not know who shot him in the face. Hernandez has not been charged, but Bradley later filed a federal lawsuit against Hernandez seeking monetary damages.
"Undoubtedly, the commonwealth would like to suggest to the jury that Hernandez has a propensity for shooting his friends for one reason or another. Under this theory, if the jury finds that it was Hernandez who shot Bradley, the jury could then jump to the conclusion that it was Hernandez who shot Lloyd as well," Hernandez's lawyers wrote.
"This is precisely the kind of outlandish, flawed reasoning which our criminal justice system prohibits."
A spokesman for Bristol County prosecutors declined to comment.
Prosecutors suggested earlier that the encounters in Boston, Providence and Florida show a "common pattern" of violence by Hernandez following disputes at nightclubs.
Lloyd had been at a Boston nightclub with Hernandez and others days before his body was found about a mile from Hernandez's North Attleborough home.