WHITEFISH BAY, Wis. (CBS 58) -- An inmate has pleaded guilty to federal charges that he mailed threats to a Jewish Community Center in Whitefish Bay.

Chadwick Grubbs, 33, pleaded guilty on Tuesday afternoon.

Prosecutors say Grubbs sent threatening letters to the center three times, including in May when he was an inmate at the Winnebago County Jail.

Sheriff's Officials became aware of the threats when the letters were returned undelivered.