Two dogs were killed after being struck by a train at the weekend.
The incident occurred at around 1:30pm on Saturday, on the Paddington to Cardiff service.
The British Transport Police confirmed that a trespassing incident had taken place.
A spokesperson said: “At 1.34pm on 18 January, officers were called to the railway near Alderton following a report that a train had struck dogs on the line.
“Officers attended and following enquiries, it is believed that two dogs had been struck and killed by a train.
“Enquiries continue in relation to this incident. Anyone with information is asked to contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 238 of 18/01.”