On April 15, the real estate agent returned home to find a can of dog food carelessly strewn in her backyard and Jackson, her 3-year-old Cavalier King Charles Spaniel, sick.

"That was unusual," Kollenborn said. "When I opened the kitchen door, Jackson had thrown up all over his pillow."

Worried, she informed the police, who advised her to take Jackson to the vet if his condition worsened.

By the next morning, Jackson was acting "drunk" and could barely move. Kollenborn rushed him to the United Emergency Animal Clinic on Bascom Avenue, but it was too late. Jackson's blood tested positive for high levels of antifreeze.

In a last-ditch effort to save Jackson's life, Kollenborn moved him to the Pacific Veterinary Specialists and Emergency clinic in Capitola. On April 17, Kollenborn made the decision to euthanize Jackson. "The veterinarian called to say he was too far gone and in pain. His kidneys had failed. I didn't want him to suffer another minute," she said.

Kollenborn says she is shocked by the cruel act. No one ever filed any complaints against Jackson. Yet the threatening handwritten notes she received suggested that whoever did this had an issue with Jackson's barking. The first note she found in 2002 read: "If you don't do something about your dog's barking, I will ..." The second note, which came a year later, was also chilling: "If your dog doesn't stop barking, I'll kill your dog."

"I took the second note as a direct threat," said Kollenborn, who shared her Iris Court home with her sister until June 2004, when her sister got married and moved out. "My sister and I sent out emails and went door to door, asking neighbors if they had a problem with Jackson's barking." No one complained. Kollenborn also made sure that Jackson was not left alone for long periods of time. If she had a late appointment, her sister would dog-sit.

While grief kept her away from her Iris Court home for days, Kollenborn wants to see justice done. "Jackson was my roommate, my buddy, my date. Jackson shared my bed and went everywhere with me. Everything in the house reminds me of him," said Kollenborn, who had raised Jackson since he was a puppy.

San Jose Police Department spokesman Enrique Garcia confirmed that the police have collected evidence and are investigating this as a case of animal cruelty. Kollenborn gave the police a bag with the can of dog food and the threatening notes she'd received. San Jose Police Detective Troy Sirmons said the police are following up on leads and stepping up patrols in the area.

Kollenborn now plans to buy a lock for her backyard door and install a video monitoring and alarm system. "I don't feel safe here anymore. I feel like someone has been watching me," she said. "But I'm not going to move. If I do, that person wins, right?"

She is resolute in finding the culprit. On April 21, she organized an open house for neighbors to spread the word and pass out flyers in the hope of getting more leads on who killed Jackson. Her family is offering a $1,000 reward for anyone who comes forward with information.

The news shocked neighbors who live on Iris Court. Residents consider it a "close-knit" neighborhood. "I felt sick," said Heather Hoffman, who lives a house away. "This was a slow and painful death."

After the incident neighbors discovered that other residents on Iris Court have also received anonymous notes over the past year. Hoffman, also a dog owner, recalled finding a note left in her yard in 2002 that said, "Your dog keeps barking. Keep your dog quiet." Now, she will keep her dog indoors at all times.

Another longtime Iris Court resident, Susan Russi, found a note taped to her cat's collar about eight years ago that said: "Keep your cat out of my yard. Otherwise I'll take care of it." Shortly after, her cat died of poisoning, though Russi cannot remember what caused it. "I haven't thought about this in a long time. It might be the same person," Russi added.

Kollenborn does not plan to get another dog, for fear that the same thing might happen again. Kollenborn just wants the person who killed her dog to know that she will find them.

United Emergency Animal Clinic veterinarian Judy Owens, who took care of Jackson, is convinced that someone poisoned him.

"I like to believe that people always have the best intentions and accidents happen because people are in the wrong place at the wrong time," she said. Yet given the given the circumstances--the threatening notes, the high levels of antifreeze in his blood, the can of dog food in the backyard that was not placed there by Kollenborn--Owens says she is "absolutely convinced" this wasn't an accident.

Anyone with information can contact Det. Troy Sirmons of the San Jose Police Department Bureau of Investigations at 408.277.4161. Anyone wishing to remain anonymous can call Crime Stoppers at 408.947.STOP.