Gov. Deval Patrick is urging prosecutors, defense attorneys and staff from various state departments to join forces to determine which potentially mishandled samples at a state lab pertain to people now behind bars.

In a letter on Tuesday to the Massachusetts District Attorneys Association, Patrick, a Democrat, said collaboration will be needed to “prioritize the matters of defendants currently incarcerated” because the database for this evidence contains incomplete information.

Patrick proposed creating a special unit to aid in the collaboration.

The Boston drug lab was shut down after state police discovered a chemist failed to follow protocols in drug testing, potentially exposing thousands of drug convictions to legal challenges. The lab was involved in certifying drug evidence in cases submitted by local police in dozens of communities around the state.

Patrick on Tuesday debunked claims that 13,000 samples were “on indefinite hold,” saying the State Police Crime Lab in Sudbury will now handle testing.

Patrick’s response comes just days after the association penned a letter to him urging that the state ensures “justice is done” for the cases involved in the potentially mishandled samples. The district attorneys also pushed Patrick to take steps to disclose all information relevant to the investigation into the handling and to prioritize the cases of incarcerated people.

Patrick ordered the Boston lab shut down last month. The chemist resigned in March during an internal investigation, and two supervisors have been suspended. State Attorney General Martha Coakley has launched a criminal investigation.