A man and a woman arrested over the murders of a father and son who were shot dead in two villages six miles apart have been released from police custody.
Cambridgeshire Constabulary said the man, 27, and the woman, 33, will face no further action.
The pair had been arrested at a hotel outside Cambridge and held on suspicion of conspiracy to murder, before their release on Friday.
He was arrested in the early hours of Thursday on suspicion of conspiracy to murder, and police said his vehicle was searched and a shotgun was recovered.
Officers are checking whether the firearm was legally owned.
It comes after a father and son, named locally as builder Gary Dunmore, 57, and his 32-year-old son Josh Dunmore, who also worked in the trades, died on Wednesday.
Police were called to reports of gunshots in Meridian Close, Bluntisham, just after 9pm, then to similar reports in Sutton at 9.37pm.
A 32-year-old man was found dead at an address in Bluntisham, and a 57-year-old man was found dead inside an address in Sutton.
“It’s been widely reported in the media that this may relate to a custody battle,” he said. “I can confirm that is an active line of inquiry for us.”
A floral tribute to Gary Dunmore, left outside his home in The Row, Sutton, said: “To my dear neighbour Gary.
“A man who loved his family dearly, a dear friend to all, so helpful and kind and was always around as a friend and my little odd job man.
“I’m going to miss you.”
Another tribute said: “RIP Gary. Absolutely gutted.”
A floral tribute left to Josh Dunmore in Bluntisham said: “So sad a young life to be taken like this and a little boy now with no daddy.
“Thinking of the family. RIP Josh X.”
“Our prayers are with all involved. Rest in eternal peace.”
Uniformed officers remained on duty outside both addresses on Friday morning.
A number of neighbours of Josh Dunmore said they were too upset to speak about what had happened.
Police said that post-mortem tests on the two men, who have not been formally identified, will take place at Peterborough City Hospital on Monday.
Anyone with information is asked to call police on 101, quoting Operation Scan.