Aaron Hernandez will be arraigned next week for a 2012 double murder in Boston and prosecutors are also asking for help from tattoo artists who inked Hernandez's right arm between February 2012 and June 2013.
Prosecutors said the Bristol, Connecticut, native and former New England Patriots player is suspected of shooting Daniel de Abreu and Safiro Furtado as they sat in a car in Boston's South End in July 2012 after a chance encounter at a nightclub.
Hernandez is in prison, awaiting a trial on a separate murder charge. He is suspected in the murder of Odin Lloyd, whose body was found near Hernandez's Massachusetts home in June 2013.
Hernandez has pleaded not guilty in that case.
Officials have not said whether they believe there is any connection between the two cases.
Prosecutors said they are asking for help from tattoo artists who inked Hernandez's right arm between February 2012 and June 2013.
He is known to have traveled to Connecticut, Rhode Island, California and Florida during that period.
The tattoo artists are considered witnesses, not suspects.
Hernandez is scheduled to be arraigned on the double murder charges on May 28.