"A series of indiscreet emails by a Florida police chief has revealed his belief that Trayvon Martin's killer George Zimmerman is a volatile character who is "a Sandy Hook waiting to happen".

Steve Bracknell is the chief of the Lake Mary police department, which is investigating Zimmerman, 29, for allegedly threatening his estranged wife, Shellie, and his father-in-law with a gun on Monday.

In an email exchange with a Lake Mary resident critical of the department's initial decision not to arrest or charge Zimmerman, Bracknell appears to agree with the writer's description of Zimmerman, acquitted in July of murdering Martin, an unarmed black teenager, as "a ticking time bomb"."

Florida police chief: George Zimmerman is 'a Sandy Hook waiting to happen'