The gunman who killed five police officers in Dallas was “changed” by his experience in the US military, his mother has said.

Micah Johnson went from being an extrovert to a “hermit”, Delphine Johnson told The Blaze website.

“The military was not what Micah thought it would be,” she said. “He was very disappointed.”

Johnson opened fire at a protest being held over the deaths of African Americans at the hands of police.

The demonstrations, echoed nationwide, followed the police killings of Philando Castile in Minnesota and Alton Sterling in Louisiana.

Bomb-making material, rifles and a combat journal were found at the home of Johnson, who was himself killed.