The phone call that came to the police dispatcher in Marshall, Minn., last January described a horrific situation.

A man said he had taken a father and son hostage at gunpoint in their home. He said he'd already shot the father in the leg and was planning to shoot both hostages in the head.

Police descended on the address — only to discover the alert was a hoax. They would later learn that the phone call was placed by a young man who was nearly 1,200 miles away.

On Friday, Zachary Morgenstern, 19, pleaded guilty in U.S. District Court in Minneapolis, to one count of "threats to kill." In the plea agreement, Morgenstern admitted to a host of incidents of what is known in law enforcement circles as "swatting" — placing fake calls that get police to send out their swat teams.

Morgenstern lived in his grandparents' house in Cypress, Texas, a Houston suburb, executing his hoaxes over the phone and through Twitter and e-mail accounts. He tried to disguise his name with an assortment of Internet accounts.

He targeted individuals in Minnesota and in other states whom he got to know through Twitter and Skype while playing online games such as World of Warcraft, court records show.

Morgenstern, who is white, claimed in some of his phony calls that he was the victim of vicious hostage takers who were black.

He could face four to five years in prison under federal guidelines.

Swatting "is dangerous to victims and a significant drain on scarce law enforcement resources," U.S. Attorney Andrew Luger said Friday. He said such incidents will not "go unanswered" by the FBI and his office.

In phone calls, e-mails and tweets, Morgenstern threatened imminent bombings and shootings at Marshall schools and reported other fake hostage incidents.

"The multiple calls to law enforcement and the Marshall High School spread fear and taxed the resources of the police department and the school," Marshall Police Chief Rob Yant said in a statement. "Even after the first couple of threats, when it appeared that they were being done as a hoax, we had to take them seriously because what if we hadn't and they turned out to be real?"

Morgenstern also targeted people in Massachusetts and Ohio, according to the plea agreement. The FBI and Marshall Police Department conducted the investigation.

The plea agreement spells out a series of incidents between October 2014 and May 2015:

In an Oct. 7, 2014, call to the Marshall police dispatch center, an unidentified man who turned out to be Morgenstern claimed that he had taken two people hostage, shot one hostage in the knee cap, and planned to kill both and burn down their house unless he received a duffel bag containing half a million dollars. He also said if he saw one armed police officer, he would kill both hostages and the officer.

On Jan. 6 Morgenstern told a police dispatcher that he'd placed bombs around Marshall High School set to detonate in an hour. On Jan. 9 he called the dispatcher to say he was going "shoot up" Marshall High School in 30 minutes and kill everybody. He sent out a tweet with a similar threat. On Jan. 11 he e-mailed the Marshall school superintendent, claiming to be someone else, and saying he had planted a bomb at a Marshall school that would detonate at 10 a.m., and he would follow up by shooting students and faculty.

On Feb. 16 Morgenstern called a Marshall dispatcher, saying he was a 13-year-old boy and that two black men had just broken into his apartment and shot his mother in the leg. The caller said he was hiding in a bedroom closet and he could hear the men yelling at his mother.

Morgenstern also admitted to placing similar calls to dispatchers in Ohio and Massachusetts.

In a call to the Amesbury, Mass., police dispatch center on Feb. 10, he claimed to be a boy hiding in a closet. "He falsely stated that four black men had broken into his residence and shot his mother," according to court documents. "The call resulted in an armed police entry into the residence, after which police concluded the call was a hoax."

Morgenstern's attorney, federal public defender Andrew Mohring, could not be reached for comment. No sentencing date has been set.

Randy Furst • 612-673-4224

Twitter: @randyfurst