A murder suspect may have fled to Brighton after a mother and her baby daughter were found dead.
Detectives from Hampshire said that suspect Anthony Marsh, 21, had taken the train to Brighton before.
They warned the public not to approach him as they say he may be dangerous and carrying a knife.
He is being hunted after the bodies of his girlfriend Stephanie Bellinger, 24, and her eight-month-old daughter Lily were found at their home in Totton, Southampton.
Mr Marsh’s mother made an emotional appeal for her son to turn himself at a press conference at Southampton central police station.
A senior detective described the case as “a tragedy for all concerned” and said: “It is paramount that we trace Mr Marsh as soon as possible.”
He appealed for train passengers and taxi drivers to try to remember whether they may have seen or picked up a person fitting his description in the past few days.
Mr Marsh has not been in contact with friends or family since just before 9am on Saturday, although he has gone missing in the past and has slept rough and sheltered in churches.
He is white, 6ft 2in (1.87m) tall and has short fair hair, brown eyes, a slim build and a tattoo on his left forearm.
Witnesses are asked to contact Hampshire police.