Police have begun the DNA screening of about 2,500 men in an attempt to find the killer of a teenage model.
Sally Anne Bowman was sexually assaulted and stabbed
Sally Anne Bowman, 18, was sexually assaulted and stabbed to death yards from her home in South Croydon, south London, last September.
Police believe her killer has links to the area and have sent out leaflets asking men to volunteer for the test.
Miss Bowman's mother and two sisters urged people to come forward for the tests at Brighton Road Baptist Church.
Speaking as the DNA unit opened on Monday, Sally Anne's mother Linda said: "We're hoping that people will come in so we can eliminate them and allow more time for the police to get on with things."
She also reiterated appeals for people who may have seen items that were taken from Sally Anne's bag.
These include a white Prada handbag, Black Gucci purse which has a red and green stripe on it, a D500 Samsung phone, her passport and pictures of her niece and nephews.
Det Ch Insp Stuart Cundy, who is leading the murder investigation, said the DNA profiles would not be put onto the national database and would only be used to eliminate men from the inquiry.
He said: "What I'm appealing for is men from the South Croydon area, men who live there, work there or visit there, who were born between 1965 and 1985, that's about 20 to 40 years old, and are either white or light skinned, because that's the description of the man I believe attacked Sally Anne Bowman.
"It is an entirely voluntary process. None of those DNA samples or fingerprints will be used to check out other unsolved crimes.
"Obviously if someone does refuse then each case will be reviewed on its own merits.
"I'll look at the evidence available, how their name entered this murder inquiry and obviously we'll give careful consideration to whether someone should be arrested for Sally Anne's murder."
Jeremy Johnson, 31, was among the first volunteers to arrive at the screening centre after receiving a letter at his home.
"I feel comfortable with having the test done. I had my DNA taken when I was at university, so it's not new to me.
"It'll definitely help catch the killer," he said.
Detectives have sent 4,000 letters to homes and workplaces asking local men who match the general description of the murder suspect to go for testing.
Volunteers must not have eaten, drunk or smoked in the 20 minutes before their visit and will need to take two forms of identification.