A 24-year-old man who died after he was found seriously injured at a house in Hertfordshire had been stabbed, police said.
Darren Leonard was discovered at 11.30pm on Wednesday after police were called to reports of a disturbance at an address in the Northfield area of Hatfield.
Ambulance crews were also called to the property and Mr Leonard was taken to Lister Hospital in Stevenage, but died shortly afterwards.
A spokeswoman for Hertfordshire Police said a post-mortem examination carried out on Thursday afternoon revealed he died as a result of stab wounds.
We are determined to catch the people who killed Darren and will leave no stone unturned in order to find them.
We are keen to speak to anyone who has information about this incident. If you saw anything unusual on Wednesday evening through into the early hours of Thursday morning in that area, please get in touch with the Operation Bulrush team by calling 101."
The force spokeswoman said a significant murder inquiry is under way. Police have been carrying out house-to-house inquiries in the Northfield area and monitoring CCTV footage from local cameras, among other lines of investigation.
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The Met Office has issued a yellow cold weather alert and there's the risk of snow in places later on Boxing Day.
Mostly dry and bright, but chilly. Frost tonight.
Most places will see bright or sunny spells through the day, but with a few showers around, especially during the morning.