Houston's police chief says the U.S. Justice Department is investigating six cases over the last two years in which officers fatally shot or allegedly used excessive force against unarmed individuals.

Houston Police Chief Charles McClelland in a statement says he is confident the department's policies and procedures follow or exceed the best practices in law enforcement.

A Justice Department spokeswoman did not have any immediate comment about the investigation.

Civil rights groups applaud the investigation but also commend McClelland for his proactive efforts to provide better training to Houston police.

Three of the reviews were requested by McClelland. The others were chosen by the Department of Justice, with some pressure from community leaders.

One of the cases being investigated is the September shooting of Brian Claunch, a mentally ill one-armed, one-legged man in a wheelchair who was killed after officers said he threatened them with what turned out to be a ballpoint pen.

Another case is is that of Annika Lewis and Sebastian Prevot, who claimed they were beaten by officers during a traffic stop.

The DOJ will also review the case of Anthony Childress, who claims that he lost six teeth and needed 56 stitches after he was beaten by HPD officers.

Investigators will also look into the case of former HPD Officer Angela Horton, who was accused of striking a handcuffed robbery suspect who was apprehended at the end of the chase.

Mayor Annise Parker said no police agency is perfect and she hopes the review will make HPD better.

"I would hope that they would say we handled things appropriately and they're tragic accidents," she said.

It is not known how long it will take to complete the review. It will likely involve reviewing video, talking to witnesses and police officer.