Police are asking for the public's help in locating a man who was convicted of threatening to kill Madonna and walked away from a Los Angeles-area mental hospital last week.

Robert Hoskins, 54, is "highly psychotic" and can be extremely violent and should not be approached by members of the public, police said in a news release Thursday. They urged anyone who sees him to call authorities immediately.

Hoskins served a 10-year prison sentence for stalking and threatening Madonna after being convicted by a jury in 1996. The singer reluctantly testified against the man, who was shot by her personal security after he jumped the fence of her Hollywood Hills home.

Court records show he was convicted of vandalism in July 2011.

Police say they have searched areas where Hoskins may try to go, including the city of Long Beach south of Los Angeles, but they have been unable to find him, The Associated Press reported.