A suspected bike thief has been captured on CCTV.
Now police are asking the public to turn him in.
Sergeant Judd Hinchliffe, the investigating officer, said: “The owner of the bike had left it locked in the racks on the forecourt of the station around 11am.
“When she returned later in the day, around 6pm, she discovered both the cycle and the lock had been taken from the racks.”
The bike is a red, white and black Hardrock Sport mountain bike.
It was fitted with a child seat on the back and a basket on the front.
Sgt Hinchliffe said: “We are hoping to identify the man pictured, who had three small children in his care, and who was seen both at Brighton rail station and again leaving a train at East Croydon with a similar cycle.
“I am sure that someone will recognise him from the CCTV still.
“If you do, I would like to hear from you.
“Unfortunately, cycles are a popular target for thieves, and I would urge people to be vigilant.
“The best thing to remember is to register your bike and also to ensure a solid lock is used to secure it.
“If a bike is adequately marked, it makes it much easier to identify and therefore reduces its desirability to thieves.”
Anyone who knows the man featured in the CCTV images is asked to call British Transport Police on Freefone 0800 405040 or Crimestoppers, anonymously, on 0800 555111.