UPDATE, Thursday, 4:29 p.m. — State officials worry the mishandling of evidence at the JP lab may cause drug convictions to be overturned.

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WCVB is reporting that a chemist at the State Lab in Jamaica Plain is being investigated for tampering with evidence.

The lab tests evidence for several counties all over Massachusetts.

WBZ reports that the lab has been closed down. The station says the chemist was not trying to change the outcomes of cases.

A press conference is scheduled in Framingham at 2 p.m.

This is a breaking news story. Check back with JP Patch soon for more.