FRAMINGHAM (CBS) – A federal grand jury has begun to hand down subpoenas in its investigation of the deadly meningitis outbreak linked to a Framingham pharmacy.

Several people who worked at the New England Compounding Center are among those who have been called to testify.

Experts say it’s a sign that the feds are pursuing criminal charges against the NECC and employees who may have been negligent.

36 people have died from the outbreak, and hundreds more have gotten sick from contaminated drugs.