Teenager Brooke Anderson has recalled the devastation at seeing her family's beloved dog Jackie, the suspected victim of a baiting attack, suffer so much before eventually dying at their home in Mackay last Saturday night.

Key points: Police believe the Andersons' dogs were baited because they died after the family received threatening letters

Police believe the Andersons' dogs were baited because they died after the family received threatening letters The family says the terriers had been members of their family for 11 years

The family says the terriers had been members of their family for 11 years Glen Anderson says he's been told numerous houses in their suburb have received similar threats

"He just had a seizure again ... and then his heart was just through the roof, then all of a sudden it just stopped and he just fell over sideways," Ms Anderson said.

"That's when I just thought, he's probably not going to make it.

"You feel like you've lost someone in your family because you just know them so well."

Glen Anderson, Brooke's father, arrived home to find Jackie in an agitated state.

The family's beloved Jack Russell terrier died about 15 minutes later.

Then Mr Anderson found his other terrier, Lucky, dead the following day.

Police suspect the dogs were victims of poisoned bait because their deaths came after the Anderson family received threatening letters.

Autopsies are being carried out on Jackie and Lucky to determine the cause of death. ( Facebook: Brooke Anderson )

Senior Constable Peter Smith said weeks earlier, the owners had received two abusive and threatening letters, hand-delivered to their mailbox on Wheeler Drive, complaining about the dogs' barking.

Police could not confirm when the letters were delivered but said it was within weeks of the dogs dying.

Senior Constable Smith said it has been devastating for the owners.

"They are very distressed … this is as upsetting as it comes. To see a pet which they love responding in that way, in that pain, and to be present while that dog passes, is always going to be a distressing situation," Senior Constable Smith said.

The Anderson family received abusive letters about their dogs' barking. ( ABC News: Holly Richardson )

Mr Anderson said the terriers had been a part of their family for 11 years.

"You forget all the little things, we're going back through the photos... you definitely lose a member of your family," he said.

"You don't solve an issue through violence, you never solve issues through violence.

"We've discovered now that there's multiple houses in our suburb that have received the exact same note, so this person is quite active in their intent to harm animals.

"The dogs, they're just a major part of the kids' lives, you sort of take them with you everywhere."

Police have urged residents who lived near Wheeler Drive to be aware of the incident, especially if they had young children. ( Facebook: Brooke Anderson )

Senior Constable Smith said police had heard "gossip" relating to other incidents in the area, but said they had not received any official reports and are urging people with information to contact them.

Autopsies are being carried out on the pets to determine the cause of death.

CCTV was released, showing a person delivering a letter in July.

Dog baiting threat letters sent to home in Mackay. ( Facebook: Brooke Anderson )

Senior Constable Smith urged residents who lived near Wheeler Drive to be aware of the incident, especially if they had young children.

"The obvious risk is to your pets, but there could be young children who may be in a yard playing and they come across items which could be bait," he said.

"Something that could be handled, and that child could rub it into their eye or even put something into their mouth.

"Everyone's rightly concerned for their pets, but this is something that should also be on their radars as well."

Jackie died in her owners' arms within 15 minutes of being found sick. ( Supplied: Queensland Police Service )

A deliberate act of cruelty carries a maximum of three years' imprisonment or a $252,300 fine, under the Animal Care and Protection Act 2001.

It is also an offence to administer or feed a harmful substance, with the intention of killing an animal, with the maximum penalty $37,845 or 12 months' imprisonment.