Neighbours noticed the family home go quiet. A couple, their baby and dog were found dead.

Warning: This post discusses suicide and domestic violence, and may be distressing for some readers.

Las Vegas police officers have discovered the bodies of a Red Cross medical director, his nurse girlfriend, their infant son and the family dog this week in what is believed to have been a murder-suicide.

Neighbours of 40-year-old John Henry Lunetta and 35-year-old Karen Michelle Jackson contacted police on Monday morning after noticing the young family’s home had been quiet over the weekend.

According to the New York Post, the Las Vegas Metropolitan Police Department said the family had died in a murder-suicide believed to have been carried out by Lunetta at least a day earlier.

The couple's young son was due to celebrate his first birthday this week.

“This is deranged," neighbour Denise Bernardo said. "He must have snapped."

Neighbour Michael Bernardo agreed, telling reporters, “It was very shocking to hear.”

Jackson's 10-year-old daughter from a previous relationship, who was not present at the time of the murders, had previously complained that Lunetta was controlling.

According to the Las Vegas Journal Review, Jackson had recently completed her studies to become a nurse practitioner, and police report finding a stack of nursing textbooks inside of her car next to a baby seat.

Further information and help is available via 1800 Respect, Beyond Blue (1300 22 4636) and Lifeline (13 11 14).