Police have launched an investigation amid fears an “out-of-control” dog could kill a child after it mauled a cat to death in Hatfield.

Welwyn Hatfield Times: Shelly. Picture: Lena Masterman.Shelly. Picture: Lena Masterman. (Image: Archant)

Lena Masterman, 39, of Walker Grove, her husband Barry and their six children have been left heartbroken after their cat Shelly was killed.

Between 11am and 11.15am on Saturday, June 23, Shelly was chased down an alleyway by the family’s home and attacked by the dog, which is believed to be a white Staffordshire Bull Terrier cross Pit Bull.

The feline suffered a number of deep puncture wounds to her back legs, back and tail.

At 1am the following day, around 14 hours after the attack, Barry went into the back garden to make sure their five cats and five dogs were inside safely - a routine the family does every night before bed.

Welwyn Hatfield Times: They alleyway where the attack happened in Hatfield. Picture: Lena Masterman.They alleyway where the attack happened in Hatfield. Picture: Lena Masterman. (Image: Archant)

Barry heard strange noises and peered over the fence to discover Shelly lying in a pool of blood and crying out.

At first the family assumed she had been hit by a car, but after being seen by an emergency vet at Attimore Vets it was discovered that Shelly’s injuries were due to dog bites.

The vet also suggested that the swelling and bruising indicated that she had been swung around by her back end.

Due to not having the funds to cover the £2,000 vet bills, the family was put in touch with the Celia Hammond Animal Trust who “went above and beyond” to help Shelly.

Welwyn Hatfield Times: Shelly's blood on the pavement. Picture: Lena Masterman.Shelly's blood on the pavement. Picture: Lena Masterman. (Image: Archant)

The animal rescue charity set the family up on a pay later scheme that was manageable for them and cut the total cost back.

But after a long battle, Shelly died on Sunday, July 1.

A witness claims to have spotted a man leaving the alleyway where Shelly was found at around 11am with his dog who was “completely out of control”.

Lena said: “We are worried that this could happen to a child or our other pets.

Welwyn Hatfield Times: Shelly's blood on the pavement. Picture: Lena Masterman.Shelly's blood on the pavement. Picture: Lena Masterman. (Image: Archant)

“What breaks my heart the most is the fact that he left my fur baby to lay there in pain for 14 hours.”

A police spokeswoman said: “Police are investigating an incident of a dog being dangerously out of control in Cunningham Avenue on Saturday, June 23.

“Anyone who saw the incident, or has any other information, should contact Hertfordshire Constabulary on the non-emergency number 101, quoting crime reference 41/10617/18.”

Welwyn Hatfield Times: Shelly's blood on the pavement. Picture: Lena Masterman.Shelly's blood on the pavement. Picture: Lena Masterman. (Image: Archant)