Eyewitnesses have recalled seeing body parts spread over a road after a group was mowed down at a bus stop, leaving eight dead and a further 10 injured.
Disturbing video captured on nearby CCTV shows a silver Range Rover mounting the kerb at high speed where the group of commuters were waiting.
Some were sitting on the kerb as the bus stop does not have a bench.
The victims were mainly Venezuelan men waiting for the bus to return to the stop at 8.30am in downtown Brownsville, a city of around 185,000 in the US state of Texas.
They had been spending the night at an overnight migrant shelter, the Bishop Enrique San Pedro Ozanam Center, from where the surveillance footage was filmed.
Shelter director Victor Maldonado said the SUV ran up the kerb, flipped and continued moving for about 60 metres.
This meant people walking on the path nine metres away from the group were also hit.
Mr Maldonado said he ran outside to find a scene of horror, with body parts strewn across the road, telling CNN he is caring for a staff member “in shock”.
Witnesses apprehended the driver as he tried to run away and held him until police arrived.
The reason for the collision is not yet clear, with police investigating the cause.
Brownsville police investigator Martin Sandoval has said the driver has been “uncooperative”.
The driver was hospitalised with injuries sustained in the horror incident and police did not immediately know his name or age.
“He’s being very uncooperative at the hospital, but he will be transported to our city jail as soon as he gets released,” Mr Sandoval said of the driver.