USA TODAY NETWORK-Wisconsin

Manitowoc County Sheriff's Department has received a few death threats and a lot of hate mail since the release of "Making a Murderer."

Following the Dec. 18 release of the 10-episode Netflix series about Manitowoc County man Steven Avery's murder conviction, the department has received hundreds of emails and phone calls. Most have been what Sheriff Robert Hermann considers "more mean than anything," but some were serious.

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"One of our officers has actually gotten a couple calls that were threatening in nature," he said. "The one had indicated they should just put a bullet in their head. If not, they’re going to come and do it for them. I believe the other one was something … that actually threatened the officer and his family. (Those are) somewhat more disturbing."

Related: “Makng a Murderer” coverage, archived stories and more

Avery was cleared of a 1985 rape conviction after serving 18 years in prison following the discovery of new evidence that linked the crime to another man. About two years after his 2003 release, Avery and his teenage nephew, Brendan Dassey, were accused and later convicted of killing 25-year-old freelance photographer Teresa Halbach on the family's auto salvage yard near Mishicot.

"Making a Murderer" alleges law enforcement and the court system mishandled the case and questions whether evidence may have been planted to frame Avery.

RELATED:Who's who in the Steven Avery case

One deputy with the sheriff's department — along with former Calumet County's District Attorney Ken Kratz, who prosecuted the case, and others involved with the Avery investigation — were mailed "glitter bombs," a spring-loaded tube that shoots out glitter when opened.

Hermann said the department contacted the U.S. Postal Inspection Service and FBI to identify what the item was and where it came from before opening it. Officials determined the glitter bombs came from a company in Utah and were ordered by a man in New York.

Timeline: History of the Steven Avery case

A note was included inside the package stating, "For Steven Avery."

"We’re remaining vigilant and monitoring the mail and everything because you don’t know what you can get," Hermann said.

The department also is preparing for a protest scheduled later this month.

According to The Steven Avery Project, a group supporting Avery and Dassey, the event is scheduled for 10 a.m., Jan. 29, near the Manitowoc County Courthouse.

Hermann doesn't know how many people are expected to attend, but says the department will work with the city of Manitowoc Police Department as the event nears.

The sheriff's department still is receiving calls and emails consistently, maybe 20 to 30 daily.

"But I think they’ve diminished from what they originally were," Hermann said.