Zachary Frost, age 27, of 1632 New Boston Road, Francestown

NASHUA – A former employee of a Nashua physical therapy practice was the target recently of several threatening letters, one of which rose to the level of a felony witness-tampering charge against the suspect, Francestown resident Zachary Frost, according to police.

Frost, 27, of 1632 New Boston Road, was taken into custody Friday evening by Nashua police patrol officers, roughly three weeks after police were called to the Center for Physical Therapy, 522 Amherst St., by someone reporting the business had received “several threatening letters” addressed to an employee who had previously worked at the practice, according to police.

An investigation by detectives with the department’s Criminal Investigation Division determined that the letters had been sent from the Hillsborough County Department of Corrections, and allegedly by Frost, police said.

Detectives subsequently issued a warrant for Frost’s arrest on one count of tampering with a witness, a class B felony, and four counts of criminal threatening, Class A misdemeanors.

The tampering charge alleges that Frost sent one of the letters while knowing there was “an open investigation,” police said.

According to court records, Frost has a history of arrests, mainly on drug-related allegations, including an October 2016 arrest on nine charges: five counts of “presenting self as a pharmacist etc,” three counts of violating the controlled drug act and one count of obtaining drugs by fraud or deceit, according to his case summary.

About four months later, in early 2017, the record shows that all the counts were dismissed without prejudice.

The summaries also show that Frost reached plea agreements with prosecutors in two other cases. He was given a suspended sentence in one of them, but it’s not clear if he served time in the other.

How long Frost has been incarcerated also isn’t clear. Police did say that after he was booked on the charges from Friday’s arrest, he refused bail, and remained incarcerated pending arraignment.

That proceeding will take place in Hillsborough County Superior Court South at a date that’s yet to be determined.

Dean Shalhoup may be reached at 594-1256 or dshalhoup@nashuatelegraph.com.