Nathan Paton, 22, was discovered wandering the streets covered in blood in Borrowash, Derbyshire, on Friday.
The attack is being linked to the death of his mother Claire Nagle, 38, who died in hospital after being found seriously injured at a house nearby.
The death of a man on the M1 is connected to both attacks, police said.
More on this story and other news in Derbyshire
Vincent Nagle, 44, died after being hit by a lorry, leaving hundreds of drivers stranded on the motorway near Trowell services.
Officers said they were not looking for anyone else in connection with the investigation into all three incidents.
Mr Paton, who raised the alarm about his mother, was helped by a number of people in Borrowash.
Taz Daley, a tattooist at Equinox Tattoo in Nottingham Road, was one of the first people to speak to him.
Mr Daley said: "He had been shot twice with a nail gun.
"He was extensively cut, he'd lost a lot of blood. He had a couple of puncture wounds under his neck. He had one in his arm. It was horrific.
"He was conscious throughout, that was the amazing thing.
"We just tried to keep him talking. Kept asking his name, where he lived, how old he was, anything repetitive just to keep him awake, keep him calm until the paramedics got there."
Mrs Nagle's father, Martin Paton, said the family were "devastated" by her death.
He said: "We believe this was a tragic incident for everyone involved and their families.
"We don't want to apportion any blame and wish to be left alone to grieve as a family."
A man who was badly injured in one of several violent incidents on Friday said he had been attacked with a nail gun.