COPPELL, Texas -- The mayor of an upscale Dallas suburb apparently shot her teenage daughter to death before fatally shooting herself, after leaving notes at their home warning officers about the scene they would find and outlining how to manage family affairs, police said Wednesday.

An envelope taped to the front door of Mayor Jayne Peters' home contained a key to the house and a typed note advising police they would discover something unpleasant inside, Coppell Deputy Police Chief Steve Thomas said.

Three other notes contained instructions for handling affairs, such as taking care of the family dogs, but did not provide explanations for the deaths of the 55-year-old Peters and her 19-year-old daughter, Corinne.

"It appeared to me that there had been some thought," Thomas said.

Police found the bodies Tuesday after the mayor failed to show up at a city council meeting. They said the Dallas County Medical Examiner's Office ruled Wednesday that the case should be officially classified as a homicide-suicide investigation.

"Forensic tests (and) procedures performed point to Corinne being the victim in this tragedy, with Mayor Peters subsequently taking her own life," police said in a statement. "Both of the fatal injuries are a result of a single gun shot wounds."

Thomas said the weapon was a semiautomatic handgun and there were no signs of a struggle.

"Everybody in the room is like, 'Did we miss a sign?"' Bob Mahalik, mayor pro tem who is now acting mayor of the city, said of council members' reaction to the deaths. "It's hard to wrap your arms around it."

Mahalik said he had a gut feeling something wasn't right when the mayor didn't turn up for the meeting.

"But nowhere in your wildest dreams did you think it would be that far not right," he said.

A small collection of flowers, wreaths and cards decorated the front porch of the Peters' 3,850 square-foot brick home, where the mayor and her daughter lived alone. A printed letter said: "Please know that you are loved no matter what happens. I know that God is with you and giving you comfort. You both are with Don, a wonderful husband and father. A family again."

The mayor's husband, Donald Peters, died of cancer in 2008 at the age of 58.

Jayne Peters was a contract software developer who served as mayor of Coppell, a city of about 40,000 located 15 miles northwest of Dallas, for the past year. Her term was to expire in 2012. She had been a council member since 1998.

"This is a tremendous loss for the city, the community and the region," said City Manager Clay Phillips.

The elder Peters attended Miami University in Ohio. In her official biography on the city's website, she said "Coppell is a community with a huge heart, and we take care of one another."

"She enjoyed what she was doing as mayor and she was good at what she did," said Mahalik, who last saw Peters waving and passing out candy at the city's Independence Day parade. "She attended almost everything, every ribbon-cutting, speaking at the schools, the chamber, regional meetings."

Todd Storch, of Coppell, had known Peters for about a year. When his 13-year-old daughter died in a skiing accident in March, Peters was there for him and his family and later took a spot on the foundation he formed in his daughter's name to increase awareness for organ donation.

"She was just one of those rocks that was always there. We kind of grieved together," Storch said.

Corinne Peters graduated from Coppell High School this year. A classmate said she was bound for the University of Texas at Austin, and neighbors said the mother and daughter seemed happy.

Her Facebook page shows a smiling girl in a white top and details her interests in movies and television comedies.

"Corinne was an outstanding student and gifted dancer with a big heart," said Jessica Doty, a spokeswoman for the Coppell school district. Doty called Jayne Peters a "dedicated school volunteer."

A close friend, Ashley Johnson, said Corinne loved animals and was a phenomenal ballet dancer. There were no signs of serious strain between Corinne and her mother, Johnson said.

"Her and her mom fought sometimes, but it was like a normal teenager and mom relationship," Johnson said. "I never would have thought this would have happened."

Neighbor Diane Ianni said Corinne was excited about enrolling at Texas and frequently donned shirts with the university's logo and colors.

She said when she last saw Corinne the teen was upset about having to miss at least two different summer orientation sessions at the Austin campus, the last time because her mom was having problems with her eye and had to go to a doctor's appointment. But she said Corinne recovered and had been back to her happy self.