The FBI is helping investigate what led a Texas policeman to shoot dead a wheelchair-bound double amputee who was agitated and threatening officers with what turned out to be a ballpoint pen.
Houston police chief Charles McClelland also asked the community to "reserve judgment" on the officer and his actions at the Healing Hands group home for the mentally ill, and sought to reassure the public that all his officers were trained to deal with people with mental problems.
Community and civil rights groups say Saturday's incident is another example of problems the police department has with using excessive force.
Officer Matthew Marin shot 45-year-old Brian Claunch after responding to a call that the man, who reportedly lost two limbs in a train accident, was causing a disturbance.
Police have said Mr Claunch cornered and threatened Officer Marin, who reportedly told investigators he did not know the object in Mr Claunch's hand was a pen. John Garcia, who owns the group home, said Mr Claunch liked to draw.
Police spokeswoman Jodi Silva said she did not know if FBI assistance in officer-involved shootings was rare, but said "it's the step we're taking at this point".
The Greater Houston Coalition for Justice, a group that includes 16 local and national civil rights organisations, suggested Mr Claunch's death was part of a bigger problem at the police department. "The deeper problem is a failure to discipline for excessive force, especially in the area of shootings," said Randall Kallinen, a member of the group and a civil rights lawyer.
Mr Kallinen said he would like the shooting to spark a change in the police department regarding discipline and training of officers.
Officer Marin, a five-year veteran of the department, has been placed on three-day administrative leave. That is standard department procedure for all officer-involved shootings and Ms Silva said no unusual measures were being taken that would prevent him from returning to duty this week.
It is the second time Officer Marin has killed a suspect while on duty. In 2009, investigators said he came upon a man stabbing his neighbour to death at an apartment complex and fired when the suspect refused to drop the knife, according to the Houston Chronicle.