Brian Coopers smothers pregnant girlfriend Alisha Bromfield during wedding vacation

An Illinois man has admitted to smothering his pregnant girlfriend to death while the couple was staying at a romantic lakeside resort for a friend's wedding.

Brian M Cooper, 35, called police on Sunday and said he had left his girlfriend, Alisha N Bromfield, 21, dead in their room at the Sand Bay Beach Resort near Sturgeon Bay, Wisconsin.

Prosecutors say they plan to charge Cooper with two counts of first degree homicide-- one count for Miss Bromfield and one count for her unbo baby -- as well as one count of sexual assault. 

The murder was the first in more than 10 years for the quiet, picturesque town in northe Wisconsin, which sits on a peninsula between Green Bay and Lake Michigan.

The couple worked together at Home Depot near their home in Plainfield, Illinois. they did not live together, the Door County Daily News reports

They had traveled more than 260 miles up the lake shore to stay at the resort, which charges at least $175 a night.

On Sunday afteoon, Cooper walked into a gas station in a small town 35 miles north of the resort and called police -- calmly telling them that he had killed his girlfriend.

He stayed on the phone until officers arrived. Cooper then led investigators to his hotel room at the Sand Bay Beach Resort, where they found Miss Bromfield dead, according to the Door County sheriff.

Picturesque: The couple were staying at the Sand Bay Beach Resort in a Wisconsin vacation community

A judge set Cooper's bail at $1million.

Police have not said why he killed his girlfriend, who was six and a half months pregnant.

The last murder in Door County was on New Year's Eve 2001, when one man pierced another through the heart with a katana blade

The region is known as the 'Cape Cod of the Midwest' because its rural population of 27,000 swells by hundreds of thousands every summer as tourists flock to the shoreline resorts.