A man and woman have died after police were called to deal with reports of an assault at a hotel.
Officers, who called to the Sirhowy Arms Hotel in Argoed, Blackwood, south Wales in the early hours, used a Taser on the man, who was arrested but died while in custody, Gwent Police said.
A spokeswoman said: "A Taser was discharged and a man arrested.
"The woman was located with injuries and was later pronounced deceased.
"While under arrest the man became unresponsive. Officers and paramedics administered first aid, but he also died."
The force said it had referred the incident to the police watchdog, the Independent Police Complaints Commission.
The Welsh Ambulance Service confirmed they were called to the incident at around 1.30am, sending a paramedic in a rapid response vehicle and a crew in an emergency ambulance.
A spokeswoman said: "The man and woman were both pronounced dead at the scene."
Local councillor and Caerphilly Council deputy mayor Leon Gardiner, 81, said Argoed had been "hit for six" by the deaths.
He said: "When I went for my paper this morning, I could see the road was closed off and there were police everywhere.
"When I heard that two people had died, I couldn't believe it. Everyone is totally stunned by what has happened.
"It's a shock because Argoed is a lovely place to live and I've never known anything like this to happen here before."
Mr Gardiner added he also felt sorry for the owners the Sirhowy Arms Hotel.
"They are a lovely couple and well liked" he said. "They've done a smashing job - especially with the renovations in the past couple of years.
"It's a B&B but has been used as a hostel for homeless people. It's run magnificently."
That sentiment was also echoed by a neighbour of the Sirhowy Arms Hotel: "We've never had any problems. The people who live there are not allowed to drink or smoke in the hotel so they go down to the woods to do it.
"Sometimes there are police vans outside if there has been a fight or something, but despite that it's still a quiet street."
This afternoon, Gwent Police confirmed they were treating the death of the woman as murder and would be opening an investigation.
Details of the man and woman have not yet been released but a force spokeswoman said the dead man was 34 years old.
In the meantime forensic experts dressed in white head-to-toe overalls, are continuing to comb the area for clues while residents watch on the other side of the police cordon.
One elderly resident who declined to be named said: "People are always coming in and going out of the hostel. Often I'll see a mattress under a nearby bridge where some of them end up sleeping if they get kicked out.
"Many of the residents here don't like having a halfway house. To be honest, it spoils the area."