Police have arrested two men on suspicion of murder over shootings at a house that left three men dead and two women badly injured.
Hertfordshire Police said the pair were detained in Stevenage on Thursday night and are being questioned by detectives.
Keith Cowell, 52, and his son Matthew, 17, were shot dead at their home late on Tuesday – along with Tony Dulieu, 33, of Billericay, Essex. Two women, aged 23 and 54, were injured in the attack in Plaw Hatch Close, Bishop's Stortford.
They were in a "serious but stable" condition in hospital last night, where they are thought to be under police guard. The younger woman was named locally as Clare, Matthew Cowell's girlfriend. The older woman was said to be Keith Cowell's sister, Christine.
Police said that a three-year-old girl, named by neighbours as Clare's daughter Angel, was unharmed and is being cared for by family members.
Post-mortem examinations confirmed that Keith and Matthew Cowell died from firearms injuries, Hertfordshire Police said.
The final post-mortem examination, on Mr Dulieu was to have been carried out yesterday.
Officers said their inquiries into the shooting were "progressing" but repeated their appeals to the public for information.
Flowers have been left outside the house where the killings took place and friends have paid tribute, with many leaving messages in memory of Matthew Cowell on an internet website.
But some people who claimed to know the Cowell family painted a darker picture. One man said Keith Cowell had "upset" a lot of people. A woman said she was "not surprised" by the shootings. Detectives would say only that the attack was "targeted", but sources said the victims were known to police. Locals said the Cowell family moved to Bishop's Stortford around two years ago. Before this they lived in and around the nearby town of Buntingford.
Keith Cowell is said to have worked on building sites and as a taxi driver. Neighbours said he had also been involved in running a wine bar in Stevenage.