A nationwide hunt has begun for a man wanted in connection with the murder of a woman in Hertfordshire.
The body of 34-year-old Red Cross worker Angela Hoyt was found at her house in Hatfield on Tuesday.
Police were called to the address in Glebeland following concerns raised by Ms Hoyt's family. She is thought to have died between 22 and 24 May.
Hertfordshire Police said Ms Hoyt's ex-boyfriend Martin Collett, 35, is wanted in connection with her murder.
Police believe Mr Collett has connections in a number of places including Southampton, Bristol and Stratford-upon-Avon, but could be anywhere in the country.
Det Ch Insp Mark Ross said: "Officers urgently want to trace Mr Collett but I would like to reassure members of the public that we do not believe he is a threat to anyone.
"I would ask anyone who thinks they have seen him to contact our incident room."
In a statement released through Hertfordshire Police, Ms Hoyt's family said: "Angela was a very ambitious and driven girl.
"She had a passion for human rights and wanted to use her work to help improve the lives of those less fortunate. She had strong opinions and convictions."
Ms Hoyt had recently returned from a three-month role in Pakistan as part of her work with the Red Cross.
Officers have not yet released details of how Ms Hoyt met her death but said a post-mortem examination had taken place.
Her family said she was born in Windsor, Ontario, in Canada, before moving to the UK in 1999.
She studied journalism at the University of Wales and had been working as a public affairs and communications adviser with the International Committee of the Red Cross since February 2008.
She had travelled widely and, in the three months before her death, had been working in Islamabad, Pakistan.
Ms Hoyt moved to Hatfield a year ago when she bought her first house, on Glebelands.
Geoff Loane, head of Mission at Red Cross in London, also paid tribute to her: "Her dedication to the Red Cross, first in Canada, then in London and briefly Pakistan was inspirational. We are devastated by this news."