Investigators studying a train collision in California are examining whether one of the drivers was distracted by his mobile phone.
The driver on a train carrying 222 passengers apparently ignored a red signal, causing it to hit a freight train, rail company Metrolink has said.
Local TV has reported that the driver sent a text message before the crash.
At least 24 people were killed and 80 hurt in the collision - the deadliest train accident in the US in 15 years.
The force of the impact last Friday drove the passenger train's engine back inside the first carriage.
Firefighters had to cut through the roof of the train, which was a double-decker, removing chunks of metal piece by piece. Sniffer dogs were also brought in to try to detect signs of life.