(Note: Please be advised that this story contains graphic details in paragraph 6 that may offend some readers)

By Lenzy Krehbiel-Burton

TULSA, Okla. (Reuters) - A criminal investigation into a police officer in Oklahoma who shot and killed an unarmed black man seen on video with his hands in the air was underway, authorities said on Tuesday.

Officer Betty Shelby shot Terence Crutcher, 40, after his sport utility vehicle broke down on Friday. A lawyer for the officer told media outlets that Shelby fired her weapon after Crutcher failed to comply with commands.

Crutcher's family called the shooting a criminal act and is seeking charges. The case is the latest in a string of shootings of unarmed black men by U.S. police that have raised questions of racial bias.

In one video shot from a police helicopter, a person is heard saying Crutcher is not following instructions from police.

A voice from the helicopter then says, "that looks like a bad dude too, could be on something." An officer is seen with a weapon drawn before Crutcher drops to the ground, and a female officer can be heard on police radio saying: "shots fired."

The video shows Crutcher on his back with what appears to be blood oozing from his torso.

A separate police dash cam video also shows the officer with a weapon drawn and following Crutcher as he walks to his vehicle with his hands in the air. A pop is heard as he appears to place his hands on the vehicle and he falls a few seconds later.

Crutcher's twin sister Tiffany said her brother was a church-going man who had enrolled at Tulsa Community College to better his life. On their 40th birthday about a month ago, he sent her a text message saying he wanted to make the family proud.

"That big 'bad dude,' his life mattered," she told a news conference on Monday.

Tulsa County District Attorney Steve Kunzweiler said in a statement that the criminal investigation will be thorough and he will make sure "the facts fit the law."

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The deadly shooting gained national attention after the release on Monday of the police videos, which Tulsa Police Chief Chuck Jordan said he found "very disturbing, very difficult to watch."

On Tuesday, Democratic presidential nominee Hillary Clinton called the shooting "unbearable."

"We've got to tackle systemic racism. This horrible shooting again - how many times do we have to see this in our country?" she said on the Steve Harvey radio show.

The U.S. Justice Department has launched a separate, civil rights investigation about the use of force by officers.

Scott Wood, a lawyer for Shelby, told the Tulsa World that Crutcher ignored repeated commands from the officer and reached for his pockets even though he was told not to do so.

"He has his hands up and is facing the car and looks at Shelby, and his left hand goes through the car window, and that's when she fired her shot," said Wood, who could not be reached for comment on Tuesday.

Shelby has been placed on administrative leave. One of the officers in the helicopter is Shelby's husband, police said.

(Additional reporting by Susan Heavey in Washington; Writing by Jon Herskovitz; Editing by Colleen Jenkins and Andrew Hay)